from_basics.js - mozsearch

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/* Any copyright is dedicated to the Public Domain.

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

// Array.from copies arrays.

var src = [1, 2, 3], copy = Array.from(src);

assertEq(copy === src, false);

assertEq(Array.isArray(copy), true);

assertDeepEq(copy, src);

// Non-element properties are not copied.

var a = [0, 1];

a.name = "lisa";

assertDeepEq(Array.from(a), [0, 1]);

// It's a shallow copy.

src = [[0], [1]];

copy = Array.from(src);

assertEq(copy[0], src[0]);

assertEq(copy[1], src[1]);

// Array.from can copy non-iterable objects, if they're array-like.

src = {0: "zero", 1: "one", length: 2};

copy = Array.from(src);

assertEq(Array.isArray(copy), true);

assertDeepEq(copy, ["zero", "one"]);

// Properties past the .length are not copied.

src = {0: "zero", 1: "one", 2: "two", 9: "nine", name: "lisa", length: 2};

assertDeepEq(Array.from(src), ["zero", "one"]);

// If an object has neither an @@iterator method nor .length,

// then it's treated as zero-length.

assertDeepEq(Array.from({}), []);

// Source object property order doesn't matter.

src = {length: 2, 1: "last", 0: "first"};

assertDeepEq(Array.from(src), ["first", "last"]);

// Array.from does not preserve holes.

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

assertDeepEq(Array.from([, , 2, 3]), [undefined, undefined, 2, 3]);

assertDeepEq(Array.from([0, , , ,]), [0, undefined, undefined, undefined]);

// Even on non-iterable objects.

assertDeepEq(Array.from({length: 4}), [undefined, undefined, undefined, undefined]);

// Array.from should coerce negative lengths to zero.

assertDeepEq(Array.from({length: -1}), []);

if (typeof reportCompare === 'function')

    reportCompare(0, 0);