Initializing an Array with a Single Value

Question

Is there a more compact way to do this sort of initialization?

for (var i = 0; i < arraySize; i++) array[i] = value;

Answer 1

For efficiency, I would avoid push. So simply

for (var i = 0; i < arraySize; i++) array[i] = value; 

For IE10:

array = new Array(arraySize); 
for (var i = 0; i < arraySize; i++) array[i] = value; 

Edit: modified as discussed in the comments.

Answer 2

One short way of doing it would be:

var arr = Array(arraySize).fill(value);

Would make arr = Array [ 0, 0, 0, 0, 0 ] if arraySize == 5 and value == 0, for example.

Answer 3

This is an old question, but I use this in modern JS:

[...new Array(1000000)].map(()=>42);

Answer 4

This is not as compact but is arguably more direct.

array = Array.apply(null, new Array(arraySize)).map(function () {return value;});

Answer 5

while(arraySize--) array.push(value);

no initialization (that i know of)

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Update

Since ever posting this answer 4 years ago, people seem to keep coming back here for this answer. For benchmarking purposes I made a JSPerf with some different solutions.

The solution above here isn't the quickest, although it's short. To stick to the same short style, but with a better performance:

while(size--) array[size] = value;

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Update Feb 2016 Updated the JSPerf with a new revision with more testcases.

If performance doesn't matter and you want a one-liner:

var value = 1234, // can be replaced by a fixed value
    size  = 1000, // can be replaced by a fixed value
    array = Array.apply(null,{length: size}).map(function() { return value; });

A more performant solution (in one, dirty, line): Be aware: this replaces existsing value, size and i variables in the scope

for(var i = 0, value = 1234, size = 1000, array = new Array(1000); i < size; i++) array[i] = value;

Answer 6

I think this is nice, short and elegant:

// assuming `value` is what you want to fill the array with
// and `arraySize` is the size of the array
Array(arraySize).fill(value);