from_mapping.js - mozsearch

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/* Any copyright is dedicated to the Public Domain.

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

// If the mapfn argument to Array.from is undefined, don't map.

assertDeepEq(Array.from([3, 4, 5], undefined), [3, 4, 5]);

assertDeepEq(Array.from([4, 5, 6], undefined, Math), [4, 5, 6]);

// mapfn is called with two arguments: value and index.

var log = [];

function f() {

    log.push(Array.from(arguments));

    return log.length;

assertDeepEq(Array.from(['a', 'e', 'i', 'o', 'u'], f), [1, 2, 3, 4, 5]);

assertDeepEq(log, [['a', 0], ['e', 1], ['i', 2], ['o', 3], ['u', 4]]);

// If the object to be copied is non-iterable, mapfn is still called with two

// arguments.

log = [];

assertDeepEq(Array.from({0: "zero", 1: "one", length: 2}, f), [1, 2]);

assertDeepEq(log, [["zero", 0], ["one", 1]]);

// If the object to be copied is iterable and the constructor is not Array,

// mapfn is still called with two arguments.

log = [];

function C() {}

C.from = Array.from;

var c = new C;

c[0] = 1;

c[1] = 2;

c.length = 2;

assertDeepEq(C.from(["zero", "one"], f), c);

assertDeepEq(log, [["zero", 0], ["one", 1]]);

// The mapfn is called even if the value to be mapped is undefined.

assertDeepEq(Array.from([0, 1, , 3], String), ["0", "1", "undefined", "3"]);

var arraylike = {length: 4, "0": 0, "1": 1, "3": 3};

assertDeepEq(Array.from(arraylike, String), ["0", "1", "undefined", "3"]);

if (typeof reportCompare === 'function')

    reportCompare(0, 0);