chromevox/common/chromevox_json.js

// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

goog.provide('cvox.ChromeVoxJSON');


/**
 * @fileoverview A simple wrapper around the JSON APIs.
 * If it is possible to use the browser's built in native JSON, then
 * cvox.ChromeVoxJSON is the same as JSON.
 * If the page has its own version of JSON, cvox.ChromeVoxJSON will use its
 * own implementation (rather than the version of JSON on the page
 * which may be outdated/broken).
 */

if (!cvox.ChromeVoxJSON) {
  /**
   * @type {Object}
   */
  cvox.ChromeVoxJSON = {};
}

if (window.JSON && window.JSON.toString() == '[object JSON]') {
  cvox.ChromeVoxJSON = window.JSON;
} else {
  /*
   *  JSON implementation renamed to cvox.ChromeVoxJSON.
   *  This only gets called if the page has its own version of JSON.
   *
   *  Based on:
   *  http://www.JSON.org/json2.js
   *  2010-03-20
   *
   *  Public Domain.
   *
   *  NO WARRANTY EXPRESSED OR IMPLIED. USE AT YOUR OWN RISK.
   *
   *  See http://www.JSON.org/js.html
   */
  (function() {
    function f(n) {
      // Format integers to have at least two digits.
      return n < 10 ? '0' + n : n;
    }

    if (typeof Date.prototype.toJSON !== 'function') {

      Date.prototype.toJSON = function(key) {

        return isFinite(this.valueOf()) ?
                   this.getUTCFullYear() + '-' +
                f(this.getUTCMonth() + 1) + '-' +
                f(this.getUTCDate()) + 'T' +
                f(this.getUTCHours()) + ':' +
                f(this.getUTCMinutes()) + ':' +
                f(this.getUTCSeconds()) + 'Z' : 'null';
      };

      String.prototype.toJSON =
      Number.prototype.toJSON =
      Boolean.prototype.toJSON = function(key) {
        return /** @type {string} */ (this.valueOf());
      };
    }

    var cx = /[\u0000\u00ad\u0600-\u0604\u070f\u17b4\u17b5\u200c-\u200f\u2028-\u202f\u2060-\u206f\ufeff\ufff0-\uffff]/g,
        escapable = /[\\\"\x00-\x1f\x7f-\x9f\u00ad\u0600-\u0604\u070f\u17b4\u17b5\u200c-\u200f\u2028-\u202f\u2060-\u206f\ufeff\ufff0-\uffff]/g,
        gap,
        indent,
        meta = {    // table of character substitutions
          '\b': '\\b',
          '\t': '\\t',
          '\n': '\\n',
          '\f': '\\f',
          '\r': '\\r',
          '"' : '\\"',
          '\\': '\\\\'
        },
        rep;


    function quote(string) {

      // If the string contains no control characters, no quote characters, and
      // no backslash characters, then we can safely slap some quotes around it.
      // Otherwise we must also replace the offending characters with safe
      // escape sequences.

      escapable.lastIndex = 0;
      return escapable.test(string) ?
          '"' + string.replace(escapable, function(a) {
               var c = meta[a];
               return typeof c === 'string' ? c :
                   '\\u' + ('0000' + a.charCodeAt(0).toString(16)).slice(-4);
             }) + '"' :
             '"' + string + '"';
    }


    function str(key, holder) {

      // Produce a string from holder[key].

      var i,          // The loop counter.
          k,          // The member key.
          v,          // The member value.
          length,
          mind = gap,
          partial,
          value = holder[key];

      // If the value has a toJSON method, call it to obtain a replacement
      // value.

      if (value && typeof value === 'object' &&
              typeof value.toJSON === 'function') {
        value = value.toJSON(key);
      }

      // If we were called with a replacer function, then call the replacer to
      // obtain a replacement value.

      if (typeof rep === 'function') {
        value = rep.call(holder, key, value);
      }

      // What happens next depends on the value's type.

      switch (typeof value) {
        case 'string':
          return quote(value);

        case 'number':
          // JSON numbers must be finite. Encode non-finite numbers as null.
          return isFinite(value) ? String(value) : 'null';

        case 'boolean':
        case 'null':
          // If the value is a boolean or null, convert it to a string. Note:
          // typeof null does not produce 'null'. The case is included here in
          // the remote chance that this gets fixed someday.
          return String(value);

          // If the type is 'object', we might be dealing with an object or an
          // array or null.

        case 'object':

          // Due to a specification blunder in ECMAScript, typeof null is
          // 'object', so watch out for that case.

          if (!value) {
            return 'null';
          }

          // Make an array to hold the partial results of stringifying this
          // object value.

          gap += indent;
          partial = [];

          // Is the value an array?

          if (Object.prototype.toString.apply(value) === '[object Array]') {

            // The value is an array. Stringify every element. Use null as a
            // placeholder for non-JSON values.

            length = value.length;
            for (i = 0; i < length; i += 1) {
              partial[i] = str(i, value) || 'null';
            }

            // Join all of the elements together, separated with commas, and
            // wrap them in brackets.

            v = partial.length === 0 ? '[]' :
                    gap ? '[\n' + gap +
                            partial.join(',\n' + gap) + '\n' +
                                mind + ']' :
                          '[' + partial.join(',') + ']';
            gap = mind;
            return v;
          }

          // If the replacer is an array, use it to select the members to be
          // stringified.

          if (rep && typeof rep === 'object') {
            length = rep.length;
            for (i = 0; i < length; i += 1) {
              k = rep[i];
              if (typeof k === 'string') {
                v = str(k, value);
                if (v) {
                  partial.push(quote(k) + (gap ? ': ' : ':') + v);
                }
              }
            }
          } else {

            // Otherwise, iterate through all of the keys in the object.
            for (k in value) {
              if (Object.hasOwnProperty.call(value, k)) {
                v = str(k, value);
                if (v) {
                  partial.push(quote(k) + (gap ? ': ' : ':') + v);
                }
              }
            }
          }

          // Join all of the member texts together, separated with commas,
          // and wrap them in braces.

          v = partial.length === 0 ? '{}' :
              gap ? '{\n' + gap + partial.join(',\n' + gap) + '\n' +
                      mind + '}' : '{' + partial.join(',') + '}';
          gap = mind;
          return v;
      }
    }

    // If the JSON object does not yet have a stringify method, give it one.

    if (typeof cvox.ChromeVoxJSON.stringify !== 'function') {
      /**
       * @param {*} value Input object.
       * @param {(Array.<string>|(function(string, *) : *)|null)=} replacer
       *     Replacer array or function.
       * @param {(number|string|null)=} space Whitespace character.
       * @return {string} json string which represents jsonObj.
       */
      cvox.ChromeVoxJSON.stringify = function(value, replacer, space) {

        // The stringify method takes a value and an optional replacer, and an
        // optional space parameter, and returns a JSON text. The replacer can
        // be a function that can replace values, or an array of strings that
        // will select the keys. A default replacer method can be provided. Use
        // of the space parameter can produce text that is more easily readable.

        var i;
        gap = '';
        indent = '';

        // If the space parameter is a number, make an indent string containing
        // that many spaces.

        if (typeof space === 'number') {
          for (i = 0; i < space; i += 1) {
            indent += ' ';
          }

          // If the space parameter is a string, it will be used as the indent
          // string.

        } else if (typeof space === 'string') {
          indent = space;
        }

        // If there is a replacer, it must be a function or an array.
        // Otherwise, throw an error.

        rep = replacer;
        if (replacer && typeof replacer !== 'function' &&
            (typeof replacer !== 'object' ||
            typeof replacer.length !== 'number')) {
          throw new Error('JSON.stringify');
        }

        // Make a fake root object containing our value under the key of ''.
        // Return the result of stringifying the value.

        return str('', {'': value});
      };
    }


    // If the JSON object does not yet have a parse method, give it one.

    if (typeof cvox.ChromeVoxJSON.parse !== 'function') {
      /**
       * @param {string} text The string to parse.
       * @param {(function(string, *) : *|null)=} reviver Reviver function.
       * @return {*} The JSON object.
       */
      cvox.ChromeVoxJSON.parse = function(text, reviver) {

        // The parse method takes a text and an optional reviver function, and
        // returns a JavaScript value if the text is a valid JSON text.

        var j;

        function walk(holder, key) {

          // The walk method is used to recursively walk the resulting structure
          // so that modifications can be made.

          var k, v, value = holder[key];
          if (value && typeof value === 'object') {
            for (k in value) {
              if (Object.hasOwnProperty.call(value, k)) {
                v = walk(value, k);
                if (v !== undefined) {
                  value[k] = v;
                } else {
                  delete value[k];
                }
              }
            }
          }
          return reviver.call(holder, key, value);
        }


        // Parsing happens in four stages. In the first stage, we replace
        // certain Unicode characters with escape sequences. JavaScript handles
        // many characters incorrectly, either silently deleting them, or
        // treating them as line endings.

        text = String(text);
        cx.lastIndex = 0;
        if (cx.test(text)) {
          text = text.replace(cx, function(a) {
            return '\\u' +
                ('0000' + a.charCodeAt(0).toString(16)).slice(-4);
          });
        }

        // In the second stage, we run the text against regular expressions that
        // look for non-JSON patterns. We are especially concerned with '()' and
        // 'new' because they can cause invocation, and '=' because it can cause
        // mutation. But just to be safe, we want to reject all unexpected
        // forms.
        // We split the second stage into 4 regexp operations in order to work
        // around crippling inefficiencies in IE's and Safari's regexp engines.
        // First we replace the JSON backslash pairs with '@' (a non-JSON
        // character). Second, we replace all simple value tokens with ']'
        // characters. Third, we delete all open brackets that follow a colon or
        // comma or that begin the text. Finally, we look to see that the
        // remaining characters are only whitespace or ']' or ',' or ':' or '{'
        // or '}'. If that is so, then the text is safe for eval.

        if (/^[\],:{}\s]*$/.
        test(text.replace(/\\(?:["\\\/bfnrt]|u[0-9a-fA-F]{4})/g, '@').
        replace(/"[^"\\\n\r]*"|true|false|null|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?/g, ']').
        replace(/(?:^|:|,)(?:\s*\[)+/g, ''))) {

          // In the third stage we use the eval function to compile the text
          // into a JavaScript structure. The '{' operator is subject to a
          // syntactic ambiguity in JavaScript: it can begin a block or an
          // object literal. We wrap the text in parens to eliminate the
          // ambiguity.

          j = eval('(' + text + ')');

          // In the optional fourth stage, we recursively walk the new
          // structure, passing each name/value pair to a reviver function for
          // possible transformation.
          return typeof reviver === 'function' ? walk({'': j}, '') : j;
        }

        // If the text is not JSON parseable, then a SyntaxError is thrown.

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