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40 lines
1.3 KiB
JavaScript
40 lines
1.3 KiB
JavaScript
// Copyright (c) 2021 Rick Waldron. All rights reserved.
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// This code is governed by the license found in the LICENSE file.
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/*---
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esid: sec-array.from
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description: >
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Creates an array with length that is equal to the value of the
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length property of the given array-like, regardless of
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the presence of corresponding indices and values.
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info: |
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Array.from ( items [ , mapfn [ , thisArg ] ] )
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7. Let arrayLike be ! ToObject(items).
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8. Let len be ? LengthOfArrayLike(arrayLike).
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9. If IsConstructor(C) is true, then
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a. Let A be ? Construct(C, « 𝔽(len) »).
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10. Else,
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a. Let A be ? ArrayCreate(len).
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includes: [compareArray.js]
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---*/
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const length = 5;
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const newlyCreatedArray = Array.from({ length });
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assert.sameValue(
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newlyCreatedArray.length,
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length,
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"The newly created array's length is equal to the value of the length property for the provided array like object"
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);
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assert.compareArray(newlyCreatedArray, [undefined, undefined, undefined, undefined, undefined]);
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const newlyCreatedAndMappedArray = Array.from({ length }).map(x => 1);
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assert.sameValue(
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newlyCreatedAndMappedArray.length,
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length,
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"The newly created and mapped array's length is equal to the value of the length property for the provided array like object"
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);
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assert.compareArray(newlyCreatedAndMappedArray, [1, 1, 1, 1, 1]);
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