as-base-value.js - mozsearch

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/* Any copyright is dedicated to the Public Domain.

 * http://creativecommons.org/licenses/publicdomain/ */

// Like other primitives, symbols can be treated as objects, using object-like

// syntax: `symbol.prop` or `symbol[key]`.

//

// In ECMAScript spec jargon, this creates a Reference whose base value is a

// primitive Symbol value.

var symbols = [

    Symbol(),

    Symbol("ponies"),

    Symbol.for("sym"),

    Symbol.iterator

];

// Test accessor property, used below.

var gets, sets;

Object.defineProperty(Symbol.prototype, "prop", {

    get: function () {

        "use strict";

        gets++;

        assertEq(typeof this, "symbol");

        assertEq(this, sym);

        return "got";

},

    set: function (v) {

        "use strict";

        sets++;

        assertEq(typeof this, "symbol");

        assertEq(this, sym);

        assertEq(v, "newvalue");

});

for (var sym of symbols) {

    assertEq(sym.constructor, Symbol);

    // method on Object.prototype

    assertEq(sym.hasOwnProperty("constructor"), false);

    assertEq(sym.toLocaleString(), sym.toString()); // once .toString() exists

    // custom method monkeypatched onto Symbol.prototype

    Symbol.prototype.nonStrictMethod = function (arg) {

        assertEq(arg, "ok");

        assertEq(this instanceof Symbol, true);

        assertEq(this.valueOf(), sym);

        return 13;

};

    assertEq(sym.nonStrictMethod("ok"), 13);

    // the same, but strict mode

    Symbol.prototype.strictMethod = function (arg) {

        "use strict";

        assertEq(arg, "ok2");

        assertEq(this, sym);

        return 14;

};

    assertEq(sym.strictMethod("ok2"), 14);

    // getter/setter on Symbol.prototype

    gets = 0;

    sets = 0;

    var propname = "prop";

    assertEq(sym.prop, "got");

    assertEq(gets, 1);

    assertEq(sym[propname], "got");

    assertEq(gets, 2);

    assertEq(sym.prop = "newvalue", "newvalue");

    assertEq(sets, 1);

    assertEq(sym[propname] = "newvalue", "newvalue");

    assertEq(sets, 2);

    // non-existent property

    assertEq(sym.noSuchProp, undefined);

    var noSuchPropName = "nonesuch";

    assertEq(sym[noSuchPropName], undefined);

    // non-existent method

    assertThrowsInstanceOf(() => sym.noSuchProp(), TypeError);

    assertThrowsInstanceOf(() => sym[noSuchPropName](), TypeError);

if (typeof reportCompare === "function")

    reportCompare(0, 0);