Function has

lib/preloadjs-NEXT.js:1064–1191

(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] !== undef) {
        // 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("json-parse");
      } 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" && isExtended;
          if (stringifySupported) {
            // A test function object with a custom `toJSON` method.
            (value = function () {
              return 1;
            }).toJSON = value;
            try {
              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) === undef &&
                // IE 8 serializes `undefined` as `"undefined"`. Safari <= 5.1.7 and
                // FF 3.1b3 pass this test.
                stringify(undef) === undef &&
                // Safari <= 5.1.7 and FF 3.1b3 throw `Error`s and `TypeError`s,
                // respectively, if the value is omitted entirely.
                stringify() === undef &&
                // FF 3.1b1, 2 throw an error if the given value is not a number,
                // string, array, object, Boolean, or `null` literal. This applies to
                // objects with custom `toJSON` methods as well, unless they are nested
                // inside object or array literals. YUI 3.0.0b1 ignores custom `toJSON`
                // methods entirely.
                stringify(value) === "1" &&
                stringify([value]) == "[1]" &&
                // Prototype <= 1.6.1 serializes `[undefined]` as `"[]"` instead of
                // `"[null]"`.
                stringify([undef]) == "[null]" &&
                // YUI 3.0.0b1 fails to serialize `null` literals.
                stringify(null) == "null" &&
                // FF 3.1b1, 2 halts serialization if an array contains a function:
                // `[1, true, getClass, 1]` serializes as "[1,true,],". FF 3.1b3