Is it any way to create an array a selected size(for example 10) and immediately on the spot fill in it with some numbers specified pattern (1, 2, 3, OR 2, 4, 6 and so on) in one statement in JS?
let arr = new Array(10).fill( (a) => {a = 1; return a++; } );
console.log(arr); // Should be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10In other words can I pass a some patern or function to method fill insted of a single value.
Actually there's much nicer idiom to create ranges: a spreaded Array constructor:
[...Array(n)]
creates an array of n undefined values. To get 0..n-1, just pick its keys:
[...Array(n).keys()]
for arbitrary ranges, feed it to map:
r = [...Array(10)].map((_, i) => i + 1)
console.log(r)see here: Does JavaScript have a method like "range()" to generate an array based on supplied bounds?
old answer:
yep, you're looking for Array.from:
r = Array.from({length: 10}, (_, i) => i + 1);
console.log(r)How does this work? .from inspects its first argument (which can be any object) and picks its .length property. Then, it iterates from 0 to length - 1 and invokes the second argument with two parameters - a value (which is undefined unless the first argument contains a corresponding numeric property) and an index, which takes values from 0...length-1. In this example, we have a function that just returns an index + 1, thus giving us 1..length.
Here's a useful wrapper for the above:
let range = (from, to) => Array.from({length: to - from + 1}, _ => from++);
console.log(range(1, 10))For ES5, the idiom is Array.apply(null, {length:N}):
r = Array.apply(null, {length: 10}).map(function(_, i) {
return i + 1
})
Array.prototype.slice.call({length:10}) but it has the same behaviour as Array(10)
Array.apply(null, Array(10))Array.from does. (But it does create an array filled with undefined). So to get the Array.from you'd add .map on the end: Array.apply(null, Array(10)).map(function(_, i) { return i + 1; }); Obviously this is slightly less efficient than a real polyfill would be, as it creates and throws away two arrays.
Array.from(new Array(10), (_, i) => i) // [0, 1, 2, 3, ...]forloop, and loop unrolling if possible esdiscuss.org/topic/…