ArrayList.ensureCapacity equivalent in Javascript

Question

Is there an equivalent method in Javascript arrays or ArrayList to Java's ensureCapacity? I am translating a certain Java code containing this method to Javascript, and couldn't find any equivalent to it. Thanks in advance

• Bergi: No, there is no official one, but engines are pretty smart anyway. Some of them have an optimisation to pre-allocate memory when you assign a .length, but it doesn't make much difference.

Answer 1

It is possible to initialize an array with a specific size:

var array = new Array(n);

If your array has already been initialized you can, as mentioned in comments, set the length of the array using the length property:

array.length = n;

However, the performance gains, if any, seems negligble. Here is a thread discussing this.

• CodingIntrigue: And also set it via array.length
• elbereth: So, for instance, if I am using it this way: public Path(int initialCapacity) { tsIindexes.ensureCapacity(initialCapacity); tsJindexes.ensureCapacity(initialCapacity); } would setting it with length amount to the same thing as done here?
• Frederik Wordenskjold: Yeah, it would. But as mentioned, it is probably not necessary.

Answer 2

var fruits = ['apple', 'pineapple'];
console.log(fruits.length, fruits);//2 ["apple", "pineapple"] 
fruits.length = fruits.length + 4; //increase by 4
console.log(fruits.length, fruits);//6 ["apple", "pineapple"]

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