# Yahoo! UI Library

### json 3.0.0b1

Yahoo! UI Library > json > json-parse.js (source view)
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    /**
     * <p>The JSON module adds support for serializing JavaScript objects into
     * JSON strings and parsing JavaScript objects from strings in JSON format.</p>
     *
     * <p>The JSON namespace is added to your YUI instance including static methods
     * Y.JSON.parse(..) and Y.JSON.stringify(..).</p>
     *
     * <p>The functionality and method signatures follow the ECMAScript 5
     * specification.  In browsers with native JSON support, the native
     * implementation is used.</p>
     *
     * <p>The <code>json</code> module is a rollup of <code>json-parse</code> and
     * <code>json-stringify</code>.</p>
     *
     * <p>As their names suggest, <code>json-parse</code> adds support for parsing
     * JSON data (Y.JSON.parse) and <code>json-stringify</code> for serializing
     * JavaScript data into JSON strings (Y.JSON.stringify).  You may choose to
     * include either of the submodules individually if you don't need the
     * complementary functionality, or include the rollup for both.</p>
     *
     * @module json
     * @class JSON
     * @static
     */

    /**
     * Provides Y.JSON.parse method to accept JSON strings and return native
     * JavaScript objects.
     *
     * @module json
     * @submodule json-parse
     * @for JSON
     * @static
     */

    // All internals kept private for security reasons

        /**
         * Alias to native browser implementation of the JSON object if available.
         *
         * @property Native
         * @type {Object}
         * @private
         */
    var Native = Y.config.win.JSON,

        /**
         * Replace certain Unicode characters that JavaScript may handle incorrectly
         * during eval--either by deleting them or treating them as line
         * endings--with escape sequences.
         * IMPORTANT NOTE: This regex will be used to modify the input if a match is
         * found.
         *
         * @property _UNICODE_EXCEPTIONS
         * @type {RegExp}
         * @private
         */
        _UNICODE_EXCEPTIONS = /[\u0000\u00ad\u0600-\u0604\u070f\u17b4\u17b5\u200c-\u200f\u2028-\u202f\u2060-\u206f\ufeff\ufff0-\uffff]/g,

        /**
         * First step in the safety evaluation.  Regex used to replace all escape
         * sequences (i.e. "\\", etc) with '@' characters (a non-JSON character).
         *
         * @property _ESCAPES
         * @type {RegExp}
         * @private
         */
        _ESCAPES = /\\(?:["\\\/bfnrt]|u[0-9a-fA-F]{4})/g,

        /**
         * Second step in the safety evaluation.  Regex used to replace all simple
         * values with ']' characters.
         *
         * @property _VALUES
         * @type {RegExp}
         * @private
         */
        _VALUES  = /"[^"\\\n\r]*"|true|false|null|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?/g,

        /**
         * Third step in the safety evaluation.  Regex used to remove all open
         * square brackets following a colon, comma, or at the beginning of the
         * string.
         *
         * @property _BRACKETS
         * @type {RegExp}
         * @private
         */
        _BRACKETS = /(?:^|:|,)(?:\s*\[)+/g,

        /**
         * Final step in the safety evaluation.  Regex used to test the string left
         * after all previous replacements for invalid characters.
         *
         * @property _INVALID
         * @type {RegExp}
         * @private
         */
        _INVALID = /[^\],:{}\s]/,

        /**
         * Test for JSON string of simple data string, number, boolean, or null.
         * E.g. '"some string"', "true", "false", "null", or numbers "-123e+7"
         * This was needed for some WIP native implementations (FF3.1b2) but may be
         * unnecessary now.
         *
         * @property _SIMPLE
         * @type {RegExp}
         * @private
         */
        _SIMPLE = /^\s*(?:"[^"\\\n\r]*"|true|false|null|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?)\s*$/,

        /**
         * Replaces specific unicode characters with their appropriate \unnnn
         * format. Some browsers ignore certain characters during eval.
         *
         * @method escapeException
         * @param c {String} Unicode character
         * @return {String} the \unnnn escapement of the character
         * @private
         */
        _escapeException = function (c) {
            return '\\u'+('0000'+(+(c.charCodeAt(0))).toString(16)).slice(-4);
        },

        /**
         * Traverses nested objects, applying a reviver function to each (key,value)
         * from the scope if the key:value's containing object.  The value returned
         * from the function will replace the original value in the key:value pair.
         * If the value returned is undefined, the key will be omitted from the
         * returned object.
         *
         * @method _revive
         * @param data {MIXED} Any JavaScript data
         * @param reviver {Function} filter or mutation function
         * @return {MIXED} The results of the filtered data
         * @private
         */
        _revive = function (data, reviver) {
            var walk = function (o,key) {
                var k,v,value = o[key];
                if (value && typeof value === 'object') {
                    for (k in value) {
                        if (value.hasOwnProperty(k)) {
                            v = walk(value, k);
                            if (v === undefined) {
                                delete value[k];
                            } else {
                                value[k] = v;
                            }
                        }
                    }
                }
                return reviver.call(o,key,value);
            };

            return typeof reviver === 'function' ? walk({'':data},'') : data;
        },

        /**
         * Parse a JSON string, returning the native JavaScript representation.
         *
         * @param s {string} JSON string data
         * @param reviver {function} (optional) function(k,v) passed each key value
         *          pair of object literals, allowing pruning or altering values
         * @return {MIXED} the native JavaScript representation of the JSON string
         * @throws SyntaxError
         * @method parse
         * @static
         */
        // JavaScript implementation in lieu of native browser support.  Based on
        // the json2.js library from http://json.org
        _parse = function (s,reviver) {
            if (typeof s === 'string') {
                // Replace certain Unicode characters that are otherwise handled
                // incorrectly by some browser implementations.
                // NOTE: This modifies the input if such characters are found!
                s = s.replace(_UNICODE_EXCEPTIONS, _escapeException);

                // Test for any remaining invalid characters
                if (!_INVALID.test(s.replace(_ESCAPES,'@').
                                     replace(_VALUES,']').
                                     replace(_BRACKETS,''))) {

                    // Eval the text into a JavaScript data structure, apply any
                    // reviver function, and return
                    return _revive( eval('(' + s + ')'), reviver );
                }
            }

            throw new SyntaxError('JSON.parse');
        },

        test;

    // Test the level of native browser support
    if (Native && Object.prototype.toString.call(Native) === '[object JSON]') {
        try {
            test = Native.parse('{"x":1}', function (k,v) {return k=='x' ? 2 : v;});
            switch (test.x) {
                case 1 : // Reviver not supported
                    _parse = function (s,reviver) {
                        return _SIMPLE.test(s) ?
                                eval('(' + s + ')') :
                                _revive(Native.parse(s), reviver);
                    };
                    break;

                case 2 : // Full support
                    _parse = function (s, reviver) {
                        return Native.parse(s, reviver);
                    };
                    break;

                // default is JS implementation
            }
        }
        catch (e) {} // defer to JS implementation
    }

    Y.mix(Y.namespace('JSON'),{ parse : _parse });

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