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In JavaScript development, there are often scenarios where you need to create arrays of property length. This article summarizes several techniques for creating or populating arrays of arbitrary length that can improve your programming efficiency.

Direct fill method

Take the primitive approach of manually filling the array of the desired length.

const arr = [0.0.0];
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The for loop push () 法

Much the same as the first method, except that you use a for loop to create an array of a specific length

var len = 3;
var arr = [];
for (let i=0; i < len; i++) {
  arr.push(0);
}
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Array constructor method

var len = 3;
var arr = new Array(len);
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inArrayAfter the constructorfill()methods

var len = 3;
var arr = new Array(len).fill(0);
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If you fill() an Array with an object, all elements reference the same instance (that is, the object is not cloned multiple times, array.from () does not have this problem) :

var len = 3;
var obj = {};
var arr = new Array(len).fill(obj);
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So manipulating the array should be faster than creating it using the constructor. Creating an array is slow, however, because the engine may need to reallocate contiguous memory multiple times as the array grows.

useundefinedFill the array

Array.from({length: 3})       // [ undefined, undefined, undefined ]
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The following works only for iterable values and has a similar effect to array.from () :

[...new Array(3)]             // [ undefined, undefined, undefined ]
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useArray.from()mapping

If you provide a mapping function as its second argument, you can use array.from () to map.

Populate the array with values

Array.from({length: 3}, () = > 0)        // [0, 0, 0]
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Create arrays with unique (non-shared) objects

Array.from({length: 3}, () = > ({}))     // [{}, {}, {}]
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Creates an array with an ascending integer sequence

Array.from({length: 3}, (x, i) = > i)    // [0, 1, 2]
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Create with an arbitrary range of integers

var start = 2, end = 5;
Array.from({ length: end - start }, (x, i) = > i + start)    // [2, 3, 4]
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Another way to create an array of ascending integerskeys()

[...new Array(3).keys()]              // [0, 1, 2]
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