A complete WebIDLLexer (without tests) which is compliant with the lexer rules for WebIDL Second Edition available here http://heycam.github.io/webidl/

integer_snip.js

// integer = /-?([1-9][0-9]*|0[Xx][0-9A-Fa-f]+|0[0-7]*)/
INTEGER =
    opt:'-'? num:( DECINT / HEXINT / OCTINT )
    {
        if (opt) {
            num.string = '-' + num.string;
            num.value = -num.value;
        }
        return num;
    }

DECINT =
    first:[1-9] rest:[0-9]*
    {
        return token.createDecInteger(first, rest);
    }

HEXINT =
    '0' hex:[Xx] rest:[0-9A-Fa-f]+
    {
        return token.createHexInteger(hex, rest);
    }

OCTINT =
    '0' rest:[0-7]*
    {
        return token.createOctInteger(rest);
    }

main.js

var webIdlParser = require('./WebIDL.js');
var fs = require('fs');

fs.readFile('floats.webIDL', function (err, data) {
    if (err) {
        throw err;
    }

    var text = data.toString();
    var result = webIdlParser.parse(text);
    console.log(JSON.stringify(result, null, 4));
});

other_snip.js

// other = /[^\t\n\r 0-9A-Za-z]/
OTHER =
    val:[^\t\n\r 0-9A-Za-z]
    {
        return token.createOther(val);
    }

string_snip.js

function createString(val) {
    var tok = new token();
    tok.string = '"' + val + '"';
    tok.value = val;
    tok.type = 'string';
    return tok;
}

function flatten(ary) {
    return ary.reduce(function (prev, cur) {
        return prev + cur;
    }, "");
}

// string = /"[^"]*"/
STRING =
    '"' val:[^"]* '"'
    {
        return token.createString(token.flatten(val));
    }

tokens_snip.js

start = token+

token =
    FLOAT / INTEGER / IDENTIFIER / STRING / comment / WHITESPACE / OTHER

WebIDLLexer.pegjs

{
    function token() {
        this.value = '';
        this.type = 'error';
    }

    // Static methods on token
    Object.defineProperties(token, {
        createOther: {
            value: function createOther(val) {
                var tok = new token();
                tok.string = val;
                tok.value = val;
                tok.type = 'other';
                return tok;
            }
        },
        createSingleLineComment: {
            value: function createOther(val) {
                var tok = new token();
                tok.string = '//' + val;
                tok.value = val;
                tok.type = 'slcomment';
                return tok;
            }
        },
        createMultiLineComment: {
            value: function createOther(val) {
                var tok = new token();
                tok.string = '/*' + val + '*/'
                tok.value = val;
                tok.type = 'mlcomment';
                return tok;
            }
        },
        createWhiteSpace: {
            value: function createWhiteSpace(val) {
                var tok = new token();
                tok.string = val;
                tok.value = val;
                tok.type = 'ws';
                return tok;
            }
        },
        createString: {
            value: 
            
        },
        createIdent: {
            value: function createIdent(opt, first, rest) {
                var tok = new token();
                tok.value = (opt ? opt : '') + first + token.flatten(rest);
                tok.string = tok.value;
                tok.type = 'ident';
                return tok;
            }
        },
        createDecInteger: {
            value: function createDecInteger(first, rest) {
                var tok = new token();
                tok.string = first + token.flatten(rest);
                tok.value = parseInt(tok.string, 10);
                tok.type = 'integer';
                return tok;
            }
        },
        createHexInteger: {
            value: function createHexInteger(hex, rest) {
                var tok = new token();
                tok.string = '0' + hex + token.flatten(rest);
                tok.value = parseInt(token.flatten(rest), 16);
                tok.type = 'integer';
                return tok;
            }
        },
        createOctInteger: {
            value: function createOctInteger(rest) {
                var tok = new token();
                tok.string = '0' + token.flatten(rest);
                tok.value = parseInt(tok.string, 8);
                tok.type = 'integer';
                return tok;
            }
        },
        createFloat: {
            value: function createFloat(val) {
                var tok = new token();
                tok.string = val;
                tok.value = parseFloat(val);
                tok.type = 'float';
                return tok;
            }
        },
        flatten: {
            value: function flatten(ary) {
                return ary.reduce(function (prev, cur) {
                    return prev + cur;
                }, "");
            }
        }
    });
}

// integer = /-?([1-9][0-9]*|0[Xx][0-9A-Fa-f]+|0[0-7]*)/
// float = /-?(([0-9]+\.[0-9]*|[0-9]*\.[0-9]+)([Ee][+-]?[0-9]+)?|[0-9]+[Ee][+-]?[0-9]+)/
// identifier = /_?[A-Za-z][0-9A-Z_a-z-]*/
// string = /"[^"]*"/
// whitespace = /[\t\n\r ]+/
// comment = /\/\/.*|\/\*(.|\n)*?\*\//
// other = /[^\t\n\r 0-9A-Za-z]/

start = token+

token =
    FLOAT / INTEGER / IDENTIFIER / STRING / comment / WHITESPACE / OTHER

INTEGER =
    opt:'-'? num:( DECINT / HEXINT / OCTINT )
    {
        if (opt) {
            num.string = '-' + num.string;
            num.value = -num.value;
        }
        return num;
    }

DECINT =
    first:[1-9] rest:[0-9]*
    {
        return token.createDecInteger(first, rest);
    }

HEXINT =
    '0' hex:[Xx] rest:[0-9A-Fa-f]+
    {
        return token.createHexInteger(hex, rest);
    }

OCTINT =
    '0' rest:[0-7]*
    {
        return token.createOctInteger(rest);
    }

FLOAT =
    opt:'-'? float:(FULLFLOAT / EPSILONONLY)
    {
        return token.createFloat((opt ? opt : '') + float);
    }

FULLFLOAT =
    float:(FLOATSTART1 / FLOATSTART2) ep:EPSILON?
    {
        return float + (ep ? ep : '');
    }

FLOATSTART1 =
    left:[0-9]+ '.' right:[0-9]*
    {
        return token.flatten(left) + '.' + token.flatten(right);
    }

FLOATSTART2 =
    left:[0-9]* '.' right:[0-9]+
    {
        return token.flatten(left) + '.' + token.flatten(right);
    }

EPSILON =
    ep:[Ee] opt:[+-]? val:[0-9]+
    {
        return ep + (opt ? opt : '') + token.flatten(val);
    }

EPSILONONLY =
    first:[0-9]+ ep:[Ee] opt:[+-]? rest:[0-9]+
    {
        return token.flatten(first) + ep + (opt ? opt : '') + token.flatten(rest);
    }

IDENTIFIER =
    opt:'_'? first:[A-Za-z] rest:[0-9A-Z_a-z-]*
    {
        return token.createIdent(opt, first, rest);
    }

STRING =
    '"' val:[^"]* '"'
    {
        return token.createString(token.flatten(val));
    }

WHITESPACE =
    val:[\t\n\r ]+
    {
        return token.createWhiteSpace(token.flatten(val));
    }

comment =
    COMMENT1 / COMMENT2

COMMENT1 =
    '//' val:[^\n]*
    {
        return token.createSingleLineComment(token.flatten(val));
    }

COMMENT2 =
    '/*' val:(!'*/' .)* '*/'
    {
        // val is an array of arrays since !'*/' produces a null on success
        val = val.map(function (elem) { return elem[1]; });
        return token.createMultiLineComment(token.flatten(val));
    }

OTHER =
    val:[^\t\n\r 0-9A-Za-z]
    {
        return token.createOther(val);
    }