json/js/stringify.js

	stringify.js revision 4612c07daf3859e6ebfc408dc0ef9aed5f97f166
/**
 * Provides Y.JSON.stringify method for converting objects to JSON strings.
 *
 * @module json
 * @submodule json-stringify
 * @for JSON
 * @static
 */
var _JSON     = (Y.config.win || {}).JSON,
    Lang      = Y.Lang,
    isFunction= Lang.isFunction,
    isObject  = Lang.isObject,
    isArray   = Lang.isArray,
    _toStr    = Object.prototype.toString,
    Native    = (_toStr.call(_JSON) === '[object JSON]' && _JSON),
    useNative = !!Native,
    UNDEFINED = 'undefined',
    OBJECT    = 'object',
    NULL      = 'null',
    STRING    = 'string',
    NUMBER    = 'number',
    BOOLEAN   = 'boolean',
    DATE      = 'date',
    _allowable= {
        'undefined'        : UNDEFINED,
        'string'           : STRING,
        '[object String]'  : STRING,
        'number'           : NUMBER,
        '[object Number]'  : NUMBER,
        'boolean'          : BOOLEAN,
        '[object Boolean]' : BOOLEAN,
        '[object Date]'    : DATE,
        '[object RegExp]'  : OBJECT
    },
    EMPTY     = '',
    OPEN_O    = '{',
    CLOSE_O   = '}',
    OPEN_A    = '[',
    CLOSE_A   = ']',
    COMMA     = ',',
    COMMA_CR  = ",\n",
    CR        = "\n",
    COLON     = ':',
    COLON_SP  = ': ',
    QUOTE     = '"',

    // Regex used to capture characters that need escaping before enclosing
    // their containing string in quotes.
    _SPECIAL = /[\x00-\x07\x0b\x0e-\x1f\x7f-\x9f\u00ad\u0600-\u0604\u070f\u17b4\u17b5\u200c-\u200f\u2028-\u202f\u2060-\u206f\ufeff\ufff0-\uffff]/g,

    // Character substitution map for common escapes and special characters.
    _COMMON = [
        [/\\/g, '\\\\'],
        [/\"/g, '\\"'],
        [/\x08/g, '\\b'],
        [/\x09/g, '\\t'],
        [/\x0a/g, '\\n'],
        [/\x0c/g, '\\f'],
        [/\x0d/g, '\\r']
    ],
    _COMMON_LENGTH,

    // In-process optimization for special character escapes that haven't yet
    // been promoted to _COMMON
    _CHAR = {},

    // Per-char counter to determine if it's worth fast tracking a special
    // character escape sequence.
    _CHAR_COUNT, _CACHE_THRESHOLD;

// Utility function used to determine how to serialize a variable.
function _type(o) {
    var t = typeof o;
    return  _allowable[t] ||              // number, string, boolean, undefined
            _allowable[_toStr.call(o)] || // Number, String, Boolean, Date
            (t === OBJECT ?
                (o ? OBJECT : NULL) :     // object, array, null, misc natives
                UNDEFINED);               // function, unknown
}

// Escapes a special character to a safe Unicode representation
function _char(c) {
    if (!_CHAR[c]) {
        _CHAR[c] = '\\u'+('0000'+(+(c.charCodeAt(0))).toString(16)).slice(-4);
        _CHAR_COUNT[c] = 0;
    }

    // === to avoid this conditional for the remainder of the current operation
    if (++_CHAR_COUNT[c] === _CACHE_THRESHOLD) {
        _COMMON.push([new RegExp(c, 'g'), _CHAR[c]]);
    }

    return _CHAR[c];
}

// Enclose escaped strings in quotes
function _string(s) {
    var i, chr;

    // Preprocess the string against common characters to avoid function
    // overhead associated with replacement via function.
    for (i = 0; i < _COMMON_LENGTH; i++) {
        chr = _COMMON[i];
        s = s.replace(chr[0], chr[1]);
    }

    // original function replace for the not-as-common set of chars
    return QUOTE + s.replace(_SPECIAL, _char) + QUOTE;
}

// Adds the provided space to the beginning of every line in the input string
function _indent(s,space) {
    return s.replace(/^/gm, space);
}

// JavaScript implementation of stringify (see API declaration of stringify)
function _stringify(o,w,space) {
    if (o === undefined) {
        return undefined;
    }

    var replacer = isFunction(w) ? w : null,
        format   = _toStr.call(space).match(/String|Number/) || [],
        _date    = Y.JSON.dateToString,
        stack    = [],
        tmp,i,len;

    _COMMON_LENGTH   = _COMMON.length;
    _CHAR_COUNT      = {};
    _CACHE_THRESHOLD = Y.JSON.charCacheThreshold;

    if (replacer || !isArray(w)) {
        w = undefined;
    }

    // Ensure whitelist keys are unique (bug 2110391)
    if (w) {
        tmp = {};
        for (i = 0, len = w.length; i < len; ++i) {
            tmp[w[i]] = true;
        }
        w = tmp;
    }

    // Per the spec, strings are truncated to 10 characters and numbers
    // are converted to that number of spaces (max 10)
    space = format[0] === 'Number' ?
                new Array(Math.min(Math.max(0,space),10)+1).join(" ") :
                (space || EMPTY).slice(0,10);

    function _serialize(h,key) {
        var value = h[key],
            t     = _type(value),
            a     = [],
            colon = space ? COLON_SP : COLON,
            arr, i, keys, k, v;

        // Per the ECMA 5 spec, toJSON is applied before the replacer is
        // called.  Also per the spec, Date.prototype.toJSON has been added, so
        // Date instances should be serialized prior to exposure to the
        // replacer.  I disagree with this decision, but the spec is the spec.
        if (isObject(value) && isFunction(value.toJSON)) {
            value = value.toJSON(key);
        } else if (t === DATE) {
            value = _date(value);
        }

        if (isFunction(replacer)) {
            value = replacer.call(h,key,value);
        }

        if (value !== h[key]) {
            t = _type(value);
        }

        switch (t) {
            case DATE    : // intentional fallthrough.  Pre-replacer Dates are
                           // serialized in the toJSON stage.  Dates here would
                           // have been produced by the replacer.
            case OBJECT  : break;
            case STRING  : return _string(value);
            case NUMBER  : return isFinite(value) ? value+EMPTY : NULL;
            case BOOLEAN : return value+EMPTY;
            case NULL    : return NULL;
            default      : return undefined;
        }

        // Check for cyclical references in nested objects
        for (i = stack.length - 1; i >= 0; --i) {
            if (stack[i] === value) {
                throw new Error("JSON.stringify. Cyclical reference");
            }
        }

        arr = isArray(value);

        // Add the object to the processing stack
        stack.push(value);

        if (arr) { // Array
            for (i = value.length - 1; i >= 0; --i) {
                a[i] = _serialize(value, i) || NULL;
            }
        } else {   // Object
            // If whitelist provided, take only those keys
            keys = w || value;
            i = 0;

            for (k in keys) {
                if (keys.hasOwnProperty(k)) {
                    v = _serialize(value, k);
                    if (v) {
                        a[i++] = _string(k) + colon + v;
                    }
                }
            }
        }

        // remove the array from the stack
        stack.pop();

        if (space && a.length) {
            return arr ?
                OPEN_A + CR + _indent(a.join(COMMA_CR), space) + CR + CLOSE_A :
                OPEN_O + CR + _indent(a.join(COMMA_CR), space) + CR + CLOSE_O;
        } else {
            return arr ?
                OPEN_A + a.join(COMMA) + CLOSE_A :
                OPEN_O + a.join(COMMA) + CLOSE_O;
        }
    }

    // process the input
    return _serialize({'':o},'');
}

// Double check basic native functionality.  This is primarily to catch broken
// early JSON API implementations in Firefox 3.1 beta1 and beta2.
if ( Native ) {
    try {
        useNative = ( '0' === Native.stringify(0) );
    } catch ( e ) {
        useNative = false;
    }
}

Y.mix(Y.namespace('JSON'),{
    /**
     * Leverage native JSON stringify if the browser has a native
     * implementation.  In general, this is a good idea.  See the Known Issues
     * section in the JSON user guide for caveats.  The default value is true
     * for browsers with native JSON support.
     *
     * @property JSON.useNativeStringify
     * @type Boolean
     * @default true
     * @static
     */
    useNativeStringify : useNative,

    /**
     * Serializes a Date instance as a UTC date string.  Used internally by
     * stringify.  Override this method if you need Dates serialized in a
     * different format.
     *
     * @method dateToString
     * @param d {Date} The Date to serialize
     * @return {String} stringified Date in UTC format YYYY-MM-DDTHH:mm:SSZ
     * @deprecated Use a replacer function
     * @static
     */
    dateToString : function (d) {
        function _zeroPad(v) {
            return v < 10 ? '0' + v : v;
        }

        return d.getUTCFullYear()           + '-' +
              _zeroPad(d.getUTCMonth() + 1) + '-' +
              _zeroPad(d.getUTCDate())      + 'T' +
              _zeroPad(d.getUTCHours())     + COLON +
              _zeroPad(d.getUTCMinutes())   + COLON +
              _zeroPad(d.getUTCSeconds())   + 'Z';
    },

    /**
     * <p>Converts an arbitrary value to a JSON string representation.</p>
     *
     * <p>Objects with cyclical references will trigger an exception.</p>
     *
     * <p>If a whitelist is provided, only matching object keys will be
     * included.  Alternately, a replacer function may be passed as the
     * second parameter.  This function is executed on every value in the
     * input, and its return value will be used in place of the original value.
     * This is useful to serialize specialized objects or class instances.</p>
     *
     * <p>If a positive integer or non-empty string is passed as the third
     * parameter, the output will be formatted with carriage returns and
     * indentation for readability.  If a String is passed (such as "\t") it
     * will be used once for each indentation level.  If a number is passed,
     * that number of spaces will be used.</p>
     *
     * @method stringify
     * @param o {MIXED} any arbitrary value to convert to JSON string
     * @param w {Array|Function} (optional) whitelist of acceptable object
     *                  keys to include, or a replacer function to modify the
     *                  raw value before serialization
     * @param ind {Number|String} (optional) indentation character or depth of
     *                  spaces to format the output.
     * @return {string} JSON string representation of the input
     * @static
     */
    stringify : function (o,w,ind) {
        return Native && Y.JSON.useNativeStringify ?
            Native.stringify(o,w,ind) : _stringify(o,w,ind);
    },

    /**
     * <p>Number of occurrences of a special character within a single call to
     * stringify that should trigger promotion of that character to a dedicated
     * preprocess step for future calls.  This is only used in environments
     * that don't support native JSON, or when useNativeStringify is set to
     * false.</p>
     *
     * <p>So, if set to 50 and an object is passed to stringify that includes
     * strings containing the special character \x07 more than 50 times,
     * subsequent calls to stringify will process object strings through a
     * faster serialization path for \x07 before using the generic, slower,
     * replacement process for all special characters.</p>
     *
     * <p>To prime the preprocessor cache, set this value to 1, then call
     * <code>Y.JSON.stringify("<em>(all special characters to
     * cache)</em>");</code>, then return this setting to a more conservative
     * value.</p>
     *
     * <p>Special characters \ " \b \t \n \f \r are already cached.</p>
     *
     * @property JSON.charCacheThreshold
     * @static
     * @default 100
     * @type {Number}
     */
    charCacheThreshold: 100
});