Creating array of length n with random numbers in JavaScript

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What does Array#fill do?

According to MDN

The fill() method fills all the elements of an array from a start index to an end index with a static value.

You can use Function#apply, Array#map, Math.floor(), Math.random().

In ES6, Array#from and Arrow function can be used.

Array.from({length: 6}, () => Math.floor(Math.random() * 9));

Array.apply(null, Array(6)).map(() => Math.floor(Math.random() * 9));

var randomArr = Array.from({length: 6}, () => Math.floor(Math.random() * 9));

document.getElementById('result').innerHTML = JSON.stringify(randomArr, 0, 4); // For demo only
<pre id="result"></pre>

In ES5:

Array.apply(null, Array(6)).map(function(item, index){
    return Math.floor(Math.random() * 9);
});


var randomArr = Array.apply(null, Array(6)).map(function(item, index){
    return Math.floor(Math.random() * 9)
});

document.getElementById('result').innerHTML = JSON.stringify(randomArr, 0, 4);
<pre id="result"></pre>

What is Array.apply(null, Array(n))? Can new Array(n) used here?

Both the above code create new array of six elements, each element having value as undefined. However, when used new syntax, the created array is not iterable. To make the array iterable, Array.apply(null, Array(6)) syntax is used.

If you have lodash included on page, it’s really easy.

_.times(6, _.random.bind(0, 100))
        ^                        - Number of elements in array
                         ^       - Random number range min
                            ^^^  - Random number range max

Note: This answer is inspired from Colin Toh’s blog

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