JavaScript function similar to Python range()

Question

Is there a function in JavaScript similar to Python\'s range()?

I think there should be a better way than to write the following lines every time:

Answer 1

Can be achieved by attaching an iterator to the Number prototype

  Number.prototype[Symbol.iterator] = function* () { 
     for (var i = 0; i <= this; i++) {
       yield i
     } 
  }

[...5] // will result in [0,1,2,3,4,5]

Taken from Kyle Simpson's course Rethinking Asynchronous JavaScript

Answer 2

An option for NodeJs is to use a Buffer:

[...Buffer.alloc(5).keys()]
// [ 0, 1, 2, 3, 4 ]

What's nice is that you can iterate directly on the buffer:

Buffer.alloc(5).forEach((_, index) => console.log(index))
// 0
// 1
// 2
// 3
// 4

You can't do that with an uninitialized Array:

Array(5).forEach((_, index) => console.log(index))
// undefined

But, who in their right mind uses a Buffer for a purpose like this ;)

Answer 3

MDN recommends this approach: Sequence generator (range)

// Sequence generator function (commonly referred to as "range", e.g. Clojure, PHP etc)
const range = (start, stop, step) => Array.from({ length: (stop - start) / step + 1}, (_, i) => start + (i * step));

// Generate numbers range 0..4
console.log("range(0, 4, 1):", range(0, 4, 1));
// [0, 1, 2, 3, 4] 

// Generate numbers range 1..10 with step of 2 
console.log("\nrange(1, 10, 2):", range(1, 10, 2));
// [1, 3, 5, 7, 9]

// Generate the alphabet using Array.from making use of it being ordered as a sequence
console.log("\nrange('A'.charCodeAt(0), 'Z'.charCodeAt(0), 1).map(x => String.fromCharCode(x))", range('A'.charCodeAt(0), 'Z'.charCodeAt(0), 1).map(x => String.fromCharCode(x)));
// ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"]

Answer 4

Assuming you need a simple range with a single step:

let range = (start, end)=> {
    if(start === end) return [start];
    return [start, ...range(start + 1, end)];
}

else

let range = (start, end, step)=> {
    if(start === end) return [start];
    return [start, ...range(start + step, end)];
}

refer to here for more.

Answer 5

Still no built-in function that is equivalent to range(), but with the most recent version - ES2015 - you can build your own implementation. Here's a limited version of it. Limited because it doesn't take into account the step parameter. Just min, max.

const range = (min = null, max = null) =>
  Array.from({length:max ? max - min : min}, (v,k) => max ? k + min : k)

This is accomplished by the Array.from method able to build an array from any object that has a length property. So passing in a simple object with just the length property will create an ArrayIterator that will yield length number of objects.

Answer 6

Here you go.

This will write (or overwrite) the value of each index with the index number.

Array.prototype.writeIndices = function( n ) {
    for( var i = 0; i < (n || this.length); ++i ) this[i] = i;
    return this;
};

If you don't provide a number, it will use the current length of the Array.

Use it like this:

var array = [].writeIndices(10);  // [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]