object-prototype-tostring.js

Enable keyboard shortcuts

var toString = Object.prototype.toString;

var iter = 500;

function testConstant() {

    for (var i = 0; i < iter; i++) {

        assertEq(({}).toString(), "[object Object]");

        assertEq(toString.call([]), "[object Array]");

        assertEq(toString.call(Math.abs), "[object Function]");

testConstant();

function testOwnToStringTag() {

    var stringify = o => toString.call(o);

    var o = {};

    for (var i = 0; i < iter; i++)

        assertEq(stringify(o), "[object Object]");

    o[Symbol.toStringTag] = "foo";

    for (var i = 0; i < iter; i++)

        assertEq(stringify(o), "[object foo]");

testOwnToStringTag();

function testDynamic() {

    var arr = [{}, [], new Date, /a/];

    var expected = ["[object Object]", "[object Array]", "[object Date]", "[object RegExp]"];

    for (var i = 0; i < iter; i++) {

        for (var j = 0; j < arr.length; j++)

            assertEq(toString.call(arr[j]), expected[j]);

testDynamic();

function testToStringTagProto() {

    var c = 0;

    Object.defineProperty(Date.prototype, Symbol.toStringTag, {get() { c++; return "evil"; }});

    var arr = [{}, [], new Date, /a/];

    var expected = ["[object Object]", "[object Array]", "[object evil]", "[object RegExp]"];

    for (var i = 0; i < iter; i++) {

        for (var j = 0; j < arr.length; j++)

            assertEq(toString.call(arr[j]), expected[j]);

    assertEq(c, iter);

testToStringTagProto();