JavaScriptMinifier.php

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<?php
class JavaScriptMinifier {
 
    /* Parsing states.
     * The state machine is only necessary to decide whether to parse a slash as division
     * operator or as regexp literal.
     * States are named after the next expected item. We only distinguish states when the
     * distinction is relevant for our purpose.
     */
    const STATEMENT                = 0;
    const CONDITION                = 1;
    const PROPERTY_ASSIGNMENT      = 2;
    const EXPRESSION               = 3;
    const EXPRESSION_NO_NL         = 4; // only relevant for semicolon insertion
    const EXPRESSION_OP            = 5;
    const EXPRESSION_FUNC          = 6;
    const EXPRESSION_TERNARY       = 7; // used to determine the role of a colon
    const EXPRESSION_TERNARY_OP    = 8;
    const EXPRESSION_TERNARY_FUNC  = 9;
    const PAREN_EXPRESSION         = 10; // expression which is not on the top level
    const PAREN_EXPRESSION_OP      = 11;
    const PAREN_EXPRESSION_FUNC    = 12;
    const PROPERTY_EXPRESSION      = 13; // expression which is within an object literal
    const PROPERTY_EXPRESSION_OP   = 14;
    const PROPERTY_EXPRESSION_FUNC = 15;
 
    /* Token types */
    const TYPE_UN_OP       = 101; // unary operators
    const TYPE_INCR_OP     = 102; // ++ and --
    const TYPE_BIN_OP      = 103; // binary operators
    const TYPE_ADD_OP      = 104; // + and - which can be either unary or binary ops
    const TYPE_HOOK        = 105; // ?
    const TYPE_COLON       = 106; // :
    const TYPE_COMMA       = 107; // ,
    const TYPE_SEMICOLON   = 108; // ;
    const TYPE_BRACE_OPEN  = 109; // {
    const TYPE_BRACE_CLOSE = 110; // }
    const TYPE_PAREN_OPEN  = 111; // ( and [
    const TYPE_PAREN_CLOSE = 112; // ) and ]
    const TYPE_RETURN      = 113; // keywords: break, continue, return, throw
    const TYPE_IF          = 114; // keywords: catch, for, with, switch, while, if
    const TYPE_DO          = 115; // keywords: case, var, finally, else, do, try
    const TYPE_FUNC        = 116; // keywords: function
    const TYPE_LITERAL     = 117; // all literals, identifiers and unrecognised tokens
 
    const ACTION_GOTO = 201;
    const ACTION_PUSH = 202;
    const ACTION_POP = 203;
 
    // Sanity limit to avoid excessive memory usage
    const STACK_LIMIT = 1000;
 
    private static $maxLineLength = 1000;
 
    public static function minify( $s ) {
        // First we declare a few tables that contain our parsing rules
 
        // $opChars : Characters which can be combined without whitespace between them.
        $opChars = [
            // ECMAScript 5.1 § 7.7 Punctuators
            // Unlike the spec, these are individual symbols, not sequences.
            '{' => true,
            '}' => true,
            '(' => true,
            ')' => true,
            '[' => true,
            ']' => true,
            '.' => true,
            ';' => true,
            ',' => true,
            '<' => true,
            '>' => true,
            '=' => true,
            '!' => true,
            '+' => true,
            '-' => true,
            '*' => true,
            '%' => true,
            '&' => true,
            '|' => true,
            '^' => true,
            '~' => true,
            '?' => true,
            ':' => true,
            '/' => true,
            // ECMAScript 5.1 § 7.8.4 String Literals
            '"' => true,
            "'" => true,
        ];
 
        // $tokenTypes : Map keywords and operators to their corresponding token type
        $tokenTypes = [
            // ECMAScript 5.1 § 11.4 Unary Operators
            // ECMAScript 5.1 § 11.6 Additive Operators
            // UnaryExpression includes PostfixExpression, which includes 'new'.
            'new'        => self::TYPE_UN_OP,
            'delete'     => self::TYPE_UN_OP,
            'void'       => self::TYPE_UN_OP,
            'typeof'     => self::TYPE_UN_OP,
            '++'         => self::TYPE_INCR_OP,
            '--'         => self::TYPE_INCR_OP,
            '+'          => self::TYPE_ADD_OP,
            '-'          => self::TYPE_ADD_OP,
            '~'          => self::TYPE_UN_OP,
            '!'          => self::TYPE_UN_OP,
            // ECMAScript 5.1 § 11.5 Multiplicative Operators
            '*'          => self::TYPE_BIN_OP,
            '/'          => self::TYPE_BIN_OP,
            '%'          => self::TYPE_BIN_OP,
            // ECMAScript 5.1 § 11.7 Bitwise Shift Operators
            '<<'         => self::TYPE_BIN_OP,
            '>>'         => self::TYPE_BIN_OP,
            '>>>'        => self::TYPE_BIN_OP,
            // ECMAScript 5.1 § 11.8 Relational Operators
            '<'          => self::TYPE_BIN_OP,
            '>'          => self::TYPE_BIN_OP,
            '<='         => self::TYPE_BIN_OP,
            '>='         => self::TYPE_BIN_OP,
            // ECMAScript 5.1 § 11.9 Equality Operators
            '=='         => self::TYPE_BIN_OP,
            '!='         => self::TYPE_BIN_OP,
            '==='        => self::TYPE_BIN_OP,
            '!=='        => self::TYPE_BIN_OP,
            'instanceof' => self::TYPE_BIN_OP,
            'in'         => self::TYPE_BIN_OP,
            // ECMAScript 5.1 § 11.10 Binary Bitwise Operators
            '&'          => self::TYPE_BIN_OP,
            '^'          => self::TYPE_BIN_OP,
            '|'          => self::TYPE_BIN_OP,
            // ECMAScript 5.1 § 11.11 Binary Logical Operators
            '&&'         => self::TYPE_BIN_OP,
            '||'         => self::TYPE_BIN_OP,
            // ECMAScript 5.1 § 11.12 Conditional Operator
            // Also known as ternary.
            '?'          => self::TYPE_HOOK,
            ':'          => self::TYPE_COLON,
            // ECMAScript 5.1 § 11.13 Assignment Operators
            '='          => self::TYPE_BIN_OP,
            '*='         => self::TYPE_BIN_OP,
            '/='         => self::TYPE_BIN_OP,
            '%='         => self::TYPE_BIN_OP,
            '+='         => self::TYPE_BIN_OP,
            '-='         => self::TYPE_BIN_OP,
            '<<='        => self::TYPE_BIN_OP,
            '>>='        => self::TYPE_BIN_OP,
            '>>>='       => self::TYPE_BIN_OP,
            '&='         => self::TYPE_BIN_OP,
            '^='         => self::TYPE_BIN_OP,
            '|='         => self::TYPE_BIN_OP,
            // ECMAScript 5.1 § 11.14 Comma Operator
            ','          => self::TYPE_COMMA,
 
            // The keywords that disallow LineTerminator before their
            // (sometimes optional) Expression or Identifier.
            //
            //    keyword ;
            //    keyword [no LineTerminator here] Identifier ;
            //    keyword [no LineTerminator here] Expression ;
            //
            // See also ECMAScript 5.1:
            // - § 12.7 The continue Statement
            // - $ 12.8 The break Statement
            // - § 12.9 The return Statement
            // - § 12.13 The throw Statement
            'continue'   => self::TYPE_RETURN,
            'break'      => self::TYPE_RETURN,
            'return'     => self::TYPE_RETURN,
            'throw'      => self::TYPE_RETURN,
 
            // The keywords require a parenthesised Expression or Identifier
            // before the next Statement.
            //
            //     keyword ( Expression ) Statement
            //     keyword ( Identifier ) Statement
            //
            // See also ECMAScript 5.1:
            // - § 12.5 The if Statement
            // - § 12.6 Iteration Statements (do, while, for)
            // - § 12.10 The with Statement
            // - § 12.11 The switch Statement
            // - § 12.13 The throw Statement
            'if'         => self::TYPE_IF,
            'catch'      => self::TYPE_IF,
            'while'      => self::TYPE_IF,
            'for'        => self::TYPE_IF,
            'switch'     => self::TYPE_IF,
            'with'       => self::TYPE_IF,
 
            // The keywords followed by an Identifier, Statement,
            // Expression, or Block.
            //
            //     var Identifier
            //     else Statement
            //     do Statement
            //     case Expression
            //     try Block
            //     finally Block
            //
            // See also ECMAScript 5.1:
            // - § 12.2 Variable Statement
            // - § 12.5 The if Statement (else)
            // - § 12.6 Iteration Statements (do, while, for)
            // - § 12.11 The switch Statement (case)
            // - § 12.14 The try Statement
            'var'        => self::TYPE_DO,
            'else'       => self::TYPE_DO,
            'do'         => self::TYPE_DO,
            'case'       => self::TYPE_DO,
            'try'        => self::TYPE_DO,
            'finally'    => self::TYPE_DO,
 
            // ECMAScript 5.1 § 13 Function Definition
            'function'   => self::TYPE_FUNC,
 
            // Can be one of:
            // - DecimalLiteral (ECMAScript 5.1 § 7.8.3 Numeric Literals)
            // - MemberExpression (ECMAScript 5.1 § 11.2 Left-Hand-Side Expressions)
            '.'          => self::TYPE_BIN_OP,
 
            // Can be one of:
            // - Block (ECMAScript 5.1 § 12.1 Block)
            // - ObjectLiteral (ECMAScript 5.1 § 11.1 Primary Expressions)
            '{'          => self::TYPE_BRACE_OPEN,
            '}'          => self::TYPE_BRACE_CLOSE,
 
            // Can be one of:
            // - Parenthesised Identifier or Expression after a
            //   TYPE_IF or TYPE_FUNC keyword.
            // - PrimaryExpression (ECMAScript 5.1 § 11.1 Primary Expressions)
            // - CallExpression (ECMAScript 5.1 § 11.2 Left-Hand-Side Expressions)
            '('          => self::TYPE_PAREN_OPEN,
            ')'          => self::TYPE_PAREN_CLOSE,
 
            // Can be one of:
            // - ArrayLiteral (ECMAScript 5.1 § 11.1 Primary Expressions)
            '['          => self::TYPE_PAREN_OPEN,
            ']'          => self::TYPE_PAREN_CLOSE,
 
            // Can be one of:
            // - End of any statement
            // - EmptyStatement (ECMAScript 5.1 § 12.3 Empty Statement)
            ';'          => self::TYPE_SEMICOLON,
        ];
 
        // $model : This is the main table for our state machine. For every state/token pair
        //          the desired action is defined.
        //
        // The state pushed onto the stack by ACTION_PUSH will be returned to by ACTION_POP.
        //
        // A given state/token pair MAY NOT specify both ACTION_POP and ACTION_GOTO.
        // In the event of such mistake, ACTION_POP is used instead of ACTION_GOTO.
        $model = [
            // Statement - This is the initial state.
            self::STATEMENT => [
                self::TYPE_UN_OP => [
                    self::ACTION_GOTO => self::EXPRESSION,
                ],
                self::TYPE_INCR_OP => [
                    self::ACTION_GOTO => self::EXPRESSION,
                ],
                self::TYPE_ADD_OP => [
                    self::ACTION_GOTO => self::EXPRESSION,
                ],
                self::TYPE_BRACE_OPEN => [
                    // Use of '{' in statement context, creates a Block.
                    self::ACTION_PUSH => self::STATEMENT,
                ],
                self::TYPE_BRACE_CLOSE => [
                    // Ends a Block
                    self::ACTION_POP => true,
                ],
                self::TYPE_PAREN_OPEN => [
                    self::ACTION_PUSH => self::EXPRESSION_OP,
                    self::ACTION_GOTO => self::PAREN_EXPRESSION,
                ],
                self::TYPE_RETURN => [
                    self::ACTION_GOTO => self::EXPRESSION_NO_NL,
                ],
                self::TYPE_IF => [
                    self::ACTION_GOTO => self::CONDITION,
                ],
                self::TYPE_FUNC => [
                    self::ACTION_GOTO => self::CONDITION,
                ],
                self::TYPE_LITERAL => [
                    self::ACTION_GOTO => self::EXPRESSION_OP,
                ],
            ],
            self::CONDITION => [
                self::TYPE_PAREN_OPEN => [
                    self::ACTION_PUSH => self::STATEMENT,
                    self::ACTION_GOTO => self::PAREN_EXPRESSION,
                ],
            ],
            // Property assignment - This is an object literal declaration.
            // For example: `{ key: value }`
            self::PROPERTY_ASSIGNMENT => [
                self::TYPE_COLON => [
                    self::ACTION_GOTO => self::PROPERTY_EXPRESSION,
                ],
                self::TYPE_BRACE_OPEN => [
                    self::ACTION_PUSH => self::PROPERTY_ASSIGNMENT,
                    self::ACTION_GOTO => self::STATEMENT,
                ],
                self::TYPE_BRACE_CLOSE => [
                    self::ACTION_POP => true,
                ],
            ],
            self::EXPRESSION => [
                self::TYPE_SEMICOLON => [
                    self::ACTION_GOTO => self::STATEMENT,
                ],
                self::TYPE_BRACE_OPEN => [
                    self::ACTION_PUSH => self::EXPRESSION_OP,
                    self::ACTION_GOTO => self::PROPERTY_ASSIGNMENT,
                ],
                self::TYPE_BRACE_CLOSE => [
                    self::ACTION_POP => true,
                ],
                self::TYPE_PAREN_OPEN => [
                    self::ACTION_PUSH => self::EXPRESSION_OP,
                    self::ACTION_GOTO => self::PAREN_EXPRESSION,
                ],
                self::TYPE_FUNC => [
                    self::ACTION_GOTO => self::EXPRESSION_FUNC,
                ],
                self::TYPE_LITERAL => [
                    self::ACTION_GOTO => self::EXPRESSION_OP,
                ],
            ],
            self::EXPRESSION_NO_NL => [
                self::TYPE_SEMICOLON => [
                    self::ACTION_GOTO => self::STATEMENT,
                ],
                self::TYPE_BRACE_OPEN => [
                    self::ACTION_PUSH => self::EXPRESSION_OP,
                    self::ACTION_GOTO => self::PROPERTY_ASSIGNMENT,
                ],
                self::TYPE_BRACE_CLOSE => [
                    self::ACTION_POP => true,
                ],
                self::TYPE_PAREN_OPEN => [
                    self::ACTION_PUSH => self::EXPRESSION_OP,
                    self::ACTION_GOTO => self::PAREN_EXPRESSION,
                ],
                self::TYPE_FUNC => [
                    self::ACTION_GOTO => self::EXPRESSION_FUNC,
                ],
                self::TYPE_LITERAL => [
                    self::ACTION_GOTO => self::EXPRESSION_OP,
                ],
            ],
            self::EXPRESSION_OP => [
                self::TYPE_BIN_OP => [
                    self::ACTION_GOTO => self::EXPRESSION,
                ],
                self::TYPE_ADD_OP => [
                    self::ACTION_GOTO => self::EXPRESSION,
                ],
                self::TYPE_HOOK => [
                    self::ACTION_PUSH => self::EXPRESSION,
                    self::ACTION_GOTO => self::EXPRESSION_TERNARY,
                ],
                self::TYPE_COLON => [
                    self::ACTION_GOTO => self::STATEMENT,
                ],
                self::TYPE_COMMA => [
                    self::ACTION_GOTO => self::EXPRESSION,
                ],
                self::TYPE_SEMICOLON => [
                    self::ACTION_GOTO => self::STATEMENT,
                ],
                self::TYPE_PAREN_OPEN => [
                    self::ACTION_PUSH => self::EXPRESSION_OP,
                    self::ACTION_GOTO => self::PAREN_EXPRESSION,
                ],
                self::TYPE_BRACE_CLOSE => [
                    self::ACTION_POP => true,
                ],
            ],
            self::EXPRESSION_FUNC => [
                self::TYPE_BRACE_OPEN => [
                    self::ACTION_PUSH => self::EXPRESSION_OP,
                    self::ACTION_GOTO => self::STATEMENT,
                ],
            ],
            self::EXPRESSION_TERNARY => [
                self::TYPE_BRACE_OPEN => [
                    self::ACTION_PUSH => self::EXPRESSION_TERNARY_OP,
                    self::ACTION_GOTO => self::PROPERTY_ASSIGNMENT,
                ],
                self::TYPE_PAREN_OPEN => [
                    self::ACTION_PUSH => self::EXPRESSION_TERNARY_OP,
                    self::ACTION_GOTO => self::PAREN_EXPRESSION,
                ],
                self::TYPE_FUNC => [
                    self::ACTION_GOTO => self::EXPRESSION_TERNARY_FUNC,
                ],
                self::TYPE_LITERAL => [
                    self::ACTION_GOTO => self::EXPRESSION_TERNARY_OP,
                ],
            ],
            self::EXPRESSION_TERNARY_OP => [
                self::TYPE_BIN_OP => [
                    self::ACTION_GOTO => self::EXPRESSION_TERNARY,
                ],
                self::TYPE_ADD_OP => [
                    self::ACTION_GOTO => self::EXPRESSION_TERNARY,
                ],
                self::TYPE_HOOK => [
                    self::ACTION_PUSH => self::EXPRESSION_TERNARY,
                    self::ACTION_GOTO => self::EXPRESSION_TERNARY,
                ],
                self::TYPE_COMMA => [
                    self::ACTION_GOTO => self::EXPRESSION_TERNARY,
                ],
                self::TYPE_PAREN_OPEN => [
                    self::ACTION_PUSH => self::EXPRESSION_TERNARY_OP,
                    self::ACTION_GOTO => self::PAREN_EXPRESSION,
                ],
                self::TYPE_COLON => [
                    self::ACTION_POP => true,
                ],
            ],
            self::EXPRESSION_TERNARY_FUNC => [
                self::TYPE_BRACE_OPEN => [
                    self::ACTION_PUSH => self::EXPRESSION_TERNARY_OP,
                    self::ACTION_GOTO => self::STATEMENT,
                ],
            ],
            self::PAREN_EXPRESSION => [
                self::TYPE_BRACE_OPEN => [
                    self::ACTION_PUSH => self::PAREN_EXPRESSION_OP,
                    self::ACTION_GOTO => self::PROPERTY_ASSIGNMENT,
                ],
                self::TYPE_PAREN_OPEN => [
                    self::ACTION_PUSH => self::PAREN_EXPRESSION_OP,
                    self::ACTION_GOTO => self::PAREN_EXPRESSION,
                ],
                self::TYPE_PAREN_CLOSE => [
                    self::ACTION_POP => true,
                ],
                self::TYPE_FUNC => [
                    self::ACTION_GOTO => self::PAREN_EXPRESSION_FUNC,
                ],
                self::TYPE_LITERAL => [
                    self::ACTION_GOTO => self::PAREN_EXPRESSION_OP,
                ],
            ],
            self::PAREN_EXPRESSION_OP => [
                self::TYPE_BIN_OP => [
                    self::ACTION_GOTO => self::PAREN_EXPRESSION,
                ],
                self::TYPE_ADD_OP => [
                    self::ACTION_GOTO => self::PAREN_EXPRESSION,
                ],
                self::TYPE_HOOK => [
                    self::ACTION_GOTO => self::PAREN_EXPRESSION,
                ],
                self::TYPE_COLON => [
                    self::ACTION_GOTO => self::PAREN_EXPRESSION,
                ],
                self::TYPE_COMMA => [
                    self::ACTION_GOTO => self::PAREN_EXPRESSION,
                ],
                self::TYPE_SEMICOLON => [
                    self::ACTION_GOTO => self::PAREN_EXPRESSION,
                ],
                self::TYPE_PAREN_OPEN => [
                    self::ACTION_PUSH => self::PAREN_EXPRESSION_OP,
                    self::ACTION_GOTO => self::PAREN_EXPRESSION,
                ],
                self::TYPE_PAREN_CLOSE => [
                    self::ACTION_POP => true,
                ],
            ],
            self::PAREN_EXPRESSION_FUNC => [
                self::TYPE_BRACE_OPEN => [
                    self::ACTION_PUSH => self::PAREN_EXPRESSION_OP,
                    self::ACTION_GOTO => self::STATEMENT,
                ],
            ],
            // Property expression - The value of a key in an object literal.
            self::PROPERTY_EXPRESSION => [
                self::TYPE_BRACE_OPEN => [
                    self::ACTION_PUSH => self::PROPERTY_EXPRESSION_OP,
                    self::ACTION_GOTO => self::PROPERTY_ASSIGNMENT,
                ],
                self::TYPE_BRACE_CLOSE => [
                    self::ACTION_POP => true,
                ],
                self::TYPE_PAREN_OPEN => [
                    self::ACTION_PUSH => self::PROPERTY_EXPRESSION_OP,
                    self::ACTION_GOTO => self::PAREN_EXPRESSION,
                ],
                self::TYPE_FUNC => [
                    self::ACTION_GOTO => self::PROPERTY_EXPRESSION_FUNC,
                ],
                self::TYPE_LITERAL => [
                    self::ACTION_GOTO => self::PROPERTY_EXPRESSION_OP,
                ],
            ],
            self::PROPERTY_EXPRESSION_OP => [
                self::TYPE_BIN_OP => [
                    self::ACTION_GOTO => self::PROPERTY_EXPRESSION,
                ],
                self::TYPE_ADD_OP => [
                    self::ACTION_GOTO => self::PROPERTY_EXPRESSION,
                ],
                self::TYPE_HOOK => [
                    self::ACTION_PUSH => self::PROPERTY_EXPRESSION,
                    self::ACTION_GOTO => self::EXPRESSION_TERNARY,
                ],
                self::TYPE_COMMA => [
                    self::ACTION_GOTO => self::PROPERTY_ASSIGNMENT,
                ],
                self::TYPE_BRACE_OPEN => [
                    self::ACTION_PUSH => self::PROPERTY_EXPRESSION_OP,
                ],
                self::TYPE_BRACE_CLOSE => [
                    self::ACTION_POP => true,
                ],
                self::TYPE_PAREN_OPEN => [
                    self::ACTION_PUSH => self::PROPERTY_EXPRESSION_OP,
                    self::ACTION_GOTO => self::PAREN_EXPRESSION,
                ],
            ],
            self::PROPERTY_EXPRESSION_FUNC => [
                self::TYPE_BRACE_OPEN => [
                    self::ACTION_PUSH => self::PROPERTY_EXPRESSION_OP,
                    self::ACTION_GOTO => self::STATEMENT,
                ],
            ],
        ];
 
        // $semicolon : Rules for when a semicolon insertion is appropriate
        $semicolon = [
            self::EXPRESSION_NO_NL => [
                self::TYPE_UN_OP => true,
                self::TYPE_INCR_OP => true,
                self::TYPE_ADD_OP => true,
                self::TYPE_BRACE_OPEN => true,
                self::TYPE_PAREN_OPEN => true,
                self::TYPE_RETURN => true,
                self::TYPE_IF => true,
                self::TYPE_DO => true,
                self::TYPE_FUNC => true,
                self::TYPE_LITERAL => true
            ],
            self::EXPRESSION_OP => [
                self::TYPE_UN_OP => true,
                self::TYPE_INCR_OP => true,
                self::TYPE_BRACE_OPEN => true,
                self::TYPE_RETURN => true,
                self::TYPE_IF => true,
                self::TYPE_DO => true,
                self::TYPE_FUNC => true,
                self::TYPE_LITERAL => true
            ]
        ];
 
        // $divStates : Contains all states that can be followed by a division operator
        $divStates = [
            self::EXPRESSION_OP          => true,
            self::EXPRESSION_TERNARY_OP  => true,
            self::PAREN_EXPRESSION_OP    => true,
            self::PROPERTY_EXPRESSION_OP => true
        ];
 
        // Here's where the minifying takes place: Loop through the input, looking for tokens
        // and output them to $out, taking actions to the above defined rules when appropriate.
        $out = '';
        $pos = 0;
        $length = strlen( $s );
        $lineLength = 0;
        $newlineFound = true;
        $state = self::STATEMENT;
        $stack = [];
        $last = ';'; // Pretend that we have seen a semicolon yet
        while ( $pos < $length ) {
            // First, skip over any whitespace and multiline comments, recording whether we
            // found any newline character
            $skip = strspn( $s, " \t\n\r\xb\xc", $pos );
            if ( !$skip ) {
                $ch = $s[$pos];
                if ( $ch === '/' && substr( $s, $pos, 2 ) === '/*' ) {
                    // Multiline comment. Search for the end token or EOT.
                    $end = strpos( $s, '*/', $pos + 2 );
                    $skip = $end === false ? $length - $pos : $end - $pos + 2;
                }
            }
            if ( $skip ) {
                // The semicolon insertion mechanism needs to know whether there was a newline
                // between two tokens, so record it now.
                if ( !$newlineFound && strcspn( $s, "\r\n", $pos, $skip ) !== $skip ) {
                    $newlineFound = true;
                }
                $pos += $skip;
                continue;
            }
            // Handle C++-style comments and html comments, which are treated as single line
            // comments by the browser, regardless of whether the end tag is on the same line.
            // Handle --> the same way, but only if it's at the beginning of the line
            if ( ( $ch === '/' && substr( $s, $pos, 2 ) === '//' )
                || ( $ch === '<' && substr( $s, $pos, 4 ) === '<!--' )
                || ( $ch === '-' && $newlineFound && substr( $s, $pos, 3 ) === '-->' )
            ) {
                $pos += strcspn( $s, "\r\n", $pos );
                continue;
            }
 
            // Find out which kind of token we're handling.
            // Note: $end must point past the end of the current token
            // so that `substr($s, $pos, $end - $pos)` would be the entire token.
            // In order words, $end will be the offset of the last relevant character
            // in the stream + 1, or simply put: The offset of the first character
            // of any next token in the stream.
            $end = $pos + 1;
            // Handle string literals
            if ( $ch === "'" || $ch === '"' ) {
                // Search to the end of the string literal, skipping over backslash escapes
                $search = $ch . '\\';
                do{
                    // Speculatively add 2 to the end so that if we see a backslash,
                    // the next iteration will start 2 characters further (one for the
                    // backslash, one for the escaped character).
                    // We'll correct this outside the loop.
                    $end += strcspn( $s, $search, $end ) + 2;
                    // If the last character in our search for a quote or a backlash
                    // matched a backslash and we haven't reached the end, keep searching..
                } while ( $end - 2 < $length && $s[$end - 2] === '\\' );
                // Correction (1): Undo speculative add, keep only one (end of string literal)
                $end--;
                if ( $end > $length ) {
                    // Correction (2): Loop wrongly assumed an end quote ended the search,
                    // but search ended because we've reached the end. Correct $end.
                    // TODO: This is invalid and should throw.
                    $end--;
                }
            // We have to distinguish between regexp literals and division operators
            // A division operator is only possible in certain states
            } elseif ( $ch === '/' && !isset( $divStates[$state] ) ) {
                // Regexp literal
                for ( ; ; ) {
                    // Search until we find "/" (end of regexp), "\" (backslash escapes),
                    // or "[" (start of character classes).
                    do{
                        // Speculatively add 2 to ensure next iteration skips
                        // over backslash and escaped character.
                        // We'll correct this outside the loop.
                        $end += strcspn( $s, '/[\\', $end ) + 2;
                        // If backslash escape, keep searching...
                    } while ( $end - 2 < $length && $s[$end - 2] === '\\' );
                    // Correction (1): Undo speculative add, keep only one (end of regexp)
                    $end--;
                    if ( $end > $length ) {
                        // Correction (2): Loop wrongly assumed end slash was seen
                        // String ended without end of regexp. Correct $end.
                        // TODO: This is invalid and should throw.
                        $end--;
                        break;
                    }
                    if ( $s[$end - 1] === '/' ) {
                        break;
                    }
                    // (Implicit else), we must've found the start of a char class,
                    // skip until we find "]" (end of char class), or "\" (backslash escape)
                    do{
                        // Speculatively add 2 for backslash escape.
                        // We'll substract one outside the loop.
                        $end += strcspn( $s, ']\\', $end ) + 2;
                        // If backslash escape, keep searching...
                    } while ( $end - 2 < $length && $s[$end - 2] === '\\' );
                    // Correction (1): Undo speculative add, keep only one (end of regexp)
                    $end--;
                    if ( $end > $length ) {
                        // Correction (2): Loop wrongly assumed "]" was seen
                        // String ended without ending char class or regexp. Correct $end.
                        // TODO: This is invalid and should throw.
                        $end--;
                        break;
                    }
                }
                // Search past the regexp modifiers (gi)
                while ( $end < $length && ctype_alpha( $s[$end] ) ) {
                    $end++;
                }
            } elseif (
                $ch === '0'
                && ( $pos + 1 < $length ) && ( $s[$pos + 1] === 'x' || $s[$pos + 1] === 'X' )
            ) {
                // Hex numeric literal
                $end++; // x or X
                $len = strspn( $s, '0123456789ABCDEFabcdef', $end );
                if ( !$len ) {
                    return self::parseError(
                        $s,
                        $pos,
                        'Expected a hexadecimal number but found ' . substr( $s, $pos, 5 ) . '...'
                    );
                }
                $end += $len;
            } elseif (
                ctype_digit( $ch )
                || ( $ch === '.' && $pos + 1 < $length && ctype_digit( $s[$pos + 1] ) )
            ) {
                $end += strspn( $s, '0123456789', $end );
                $decimal = strspn( $s, '.', $end );
                if ( $decimal ) {
                    if ( $decimal > 2 ) {
                        return self::parseError( $s, $end, 'The number has too many decimal points' );
                    }
                    $end += strspn( $s, '0123456789', $end + 1 ) + $decimal;
                }
                $exponent = strspn( $s, 'eE', $end );
                if ( $exponent ) {
                    if ( $exponent > 1 ) {
                        return self::parseError( $s, $end, 'Number with several E' );
                    }
                    $end++;
 
                    // + sign is optional; - sign is required.
                    $end += strspn( $s, '-+', $end );
                    $len = strspn( $s, '0123456789', $end );
                    if ( !$len ) {
                        return self::parseError(
                            $s,
                            $pos,
                            'No decimal digits after e, how many zeroes should be added?'
                        );
                    }
                    $end += $len;
                }
            } elseif ( isset( $opChars[$ch] ) ) {
                // Punctuation character. Search for the longest matching operator.
                while (
                    $end < $length
                    && isset( $tokenTypes[substr( $s, $pos, $end - $pos + 1 )] )
                ) {
                    $end++;
                }
            } else {
                // Identifier or reserved word. Search for the end by excluding whitespace and
                // punctuation.
                $end += strcspn( $s, " \t\n.;,=<>+-{}()[]?:*/%'\"!&|^~\xb\xc\r", $end );
            }
 
            // Now get the token type from our type array
            $token = substr( $s, $pos, $end - $pos ); // so $end - $pos == strlen( $token )
            $type = $tokenTypes[$token] ?? self::TYPE_LITERAL;
 
            if ( $newlineFound && isset( $semicolon[$state][$type] ) ) {
                // This token triggers the semicolon insertion mechanism of javascript. While we
                // could add the ; token here ourselves, keeping the newline has a few advantages.
                $out .= "\n";
                $state = self::STATEMENT;
                $lineLength = 0;
            } elseif ( $lineLength + $end - $pos > self::$maxLineLength &&
                    !isset( $semicolon[$state][$type] ) && $type !== self::TYPE_INCR_OP ) {
                // This line would get too long if we added $token, so add a newline first.
                // Only do this if it won't trigger semicolon insertion and if it won't
                // put a postfix increment operator on its own line, which is illegal in js.
                $out .= "\n";
                $lineLength = 0;
            // Check, whether we have to separate the token from the last one with whitespace
            } elseif ( !isset( $opChars[$last] ) && !isset( $opChars[$ch] ) ) {
                $out .= ' ';
                $lineLength++;
            // Don't accidentally create ++, -- or // tokens
            } elseif ( $last === $ch && ( $ch === '+' || $ch === '-' || $ch === '/' ) ) {
                $out .= ' ';
                $lineLength++;
            }
            if (
                $type === self::TYPE_LITERAL
                && ( $token === 'true' || $token === 'false' )
                && ( $state === self::EXPRESSION || $state === self::PROPERTY_EXPRESSION )
                && $last !== '.'
            ) {
                $token = ( $token === 'true' ) ? '!0' : '!1';
            }
 
            $out .= $token;
            $lineLength += $end - $pos; // += strlen( $token )
            $last = $s[$end - 1];
            $pos = $end;
            $newlineFound = false;
 
            // Now that we have output our token, transition into the new state.
            if ( isset( $model[$state][$type][self::ACTION_PUSH] ) &&
                count( $stack ) < self::STACK_LIMIT
            ) {
                $stack[] = $model[$state][$type][self::ACTION_PUSH];
            }
            if ( $stack && isset( $model[$state][$type][self::ACTION_POP] ) ) {
                $state = array_pop( $stack );
            } elseif ( isset( $model[$state][$type][self::ACTION_GOTO] ) ) {
                $state = $model[$state][$type][self::ACTION_GOTO];
            }
        }
        return $out;
    }
 
    static function parseError( $fullJavascript, $position, $errorMsg ) {
        // TODO: Handle the error: trigger_error, throw exception, return false...
        return false;
    }
}