Advanced JavaScript Array Methods: fill and reverse

In addition to the basic methods forJavaScript arrays there are some new, powerful techniques for modifying array content. Like push,
pop, shift and unshift , these methods are referred to as mutators , due to the fact that they modify the array. In this article, I’ll cover two: 

fill

 and 

reverse

 .

fill

“Zeroes out” an array with any replacement value. Given an array of 

scores

 :

var scores = [15, 22, 3, 7, 11];

“Wiping out” every record in the array and viewing the result in the console:

scores.fill(0);
> [0, 0, 0, 0, 0]

fill

 can take two other arguments: the first, 

start

 is
the point from which the fill will take place. Taking the current state of 

scores

 , we can fill from the third value
with:

scores.fill(4,2);

The result:

> [0, 0, 4, 4, 4]

fill

 can also take an 

end

 value,
where the fill stops . Of course, the fill “insert” value can be anything you wish: a number, string, or 

null

 ,
for example.

fill

 is part of ES6 / JS 2015, and is therefore supported in all recent browser versions except for IE and
Opera; Mozilla Developer Network suggests a polyfill for those and older browser versions.

reverse

Pretty straightforward: 

reverse

 reverses the order of elements. Given an array

molluscs

 :

var molluscs = ["oysters", "mussels", "limpets"];

Reversing the array and showing the results in the console:

molluscs.reverse()
> ["limpets", "mussels", "oysters"]