Function has

test/json3.js:78–214

(name)

    // Internal: Determines whether the native `JSON.stringify` and `parse`
    // implementations are spec-compliant. Based on work by Ken Snyder.
    function has(name) {
      if (has[name] != null) {
        // Return cached feature test result.
        return has[name];
      }
      var isSupported;
      if (name == "bug-string-char-index") {
        // IE <= 7 doesn't support accessing string characters using square
        // bracket notation. IE 8 only supports this for primitives.
        isSupported = "a"[0] != "a";
      } else if (name == "json") {
        // Indicates whether both `JSON.stringify` and `JSON.parse` are
        // supported.
        isSupported = has("json-stringify") && has("date-serialization") && has("json-parse");
      } else if (name == "date-serialization") {
        // Indicates whether `Date`s can be serialized accurately by `JSON.stringify`.
        isSupported = has("json-stringify") && isExtended;
        if (isSupported) {
          var stringify = exports.stringify;
          attempt(function () {
            isSupported =
              // JSON 2, Prototype <= 1.7, and older WebKit builds incorrectly
              // serialize extended years.
              stringify(new Date(-8.64e15)) == '"-271821-04-20T00:00:00.000Z"' &&
              // The milliseconds are optional in ES 5, but required in 5.1.
              stringify(new Date(8.64e15)) == '"+275760-09-13T00:00:00.000Z"' &&
              // Firefox <= 11.0 incorrectly serializes years prior to 0 as negative
              // four-digit years instead of six-digit years. Credits: @Yaffle.
              stringify(new Date(-621987552e5)) == '"-000001-01-01T00:00:00.000Z"' &&
              // Safari <= 5.1.5 and Opera >= 10.53 incorrectly serialize millisecond
              // values less than 1000. Credits: @Yaffle.
              stringify(new Date(-1)) == '"1969-12-31T23:59:59.999Z"';
          });
        }
      } else {
        var value, serialized = '{"a":[1,true,false,null,"\\u0000\\b\\n\\f\\r\\t"]}';
        // Test `JSON.stringify`.
        if (name == "json-stringify") {
          var stringify = exports.stringify, stringifySupported = typeof stringify == "function";
          if (stringifySupported) {
            // A test function object with a custom `toJSON` method.
            (value = function () {
              return 1;
            }).toJSON = value;
            attempt(function () {
              stringifySupported =
                // Firefox 3.1b1 and b2 serialize string, number, and boolean
                // primitives as object literals.
                stringify(0) === "0" &&
                // FF 3.1b1, b2, and JSON 2 serialize wrapped primitives as object
                // literals.
                stringify(new Number()) === "0" &&
                stringify(new String()) == '""' &&
                // FF 3.1b1, 2 throw an error if the value is `null`, `undefined`, or
                // does not define a canonical JSON representation (this applies to
                // objects with `toJSON` properties as well, *unless* they are nested
                // within an object or array).
                stringify(getClass) === undefined &&