JavaScript - initialize array length

In this article, we would like to show you how to initialize array length in JavaScript.

In this example, we use Array() constructor to initialize an array of a given length (3) with empty values that we can't iterate on.

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var array = Array(3);

In this example, we use Array apply() with map() method to initialize an array of a given length with undefined values that we can iterate on.

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var array = Array.apply(null, Array(3)).map(function() {});

or initialized with indexes:

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var array = Array.apply(null, Array(3)).map(function(element, index) {

    return index;

});

​

console.log(array); // [ 0, 1, 2 ]

In this example, we use Array from() method to initialize array lenght and values with indexes.

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var array = Array.from({length: 3}, (value, index) => index);

​

console.log(array); // [ 0, 1, 2 ]

or all elements initialized with the same (given) value:

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var array = Array.from({ length: 3 }, () => 'value');

​

console.log(array); // [ 'value', 'value', 'value' ]

1. Array() constructor - JavaScript | MDN
2. Function.prototype.apply() - JavaScript | MDN
3. Array.prototype.map() - JavaScript | MDN
4. Array.from() - JavaScript | MDN