Does JavaScript have a method like “range()” to generate a range within the supplied bounds?

Question

In PHP, you can do...

range(1, 3); // Array(1, 2, 3)
range("A", "C"); // Array("A", "B", "C")

That is, there is a function that lets you get a range of numbers or characters by passing the upper and lower bounds.

Is there anything built-in to JavaScript natively for this? If not, how would I implement it?

Answer 1

Numbers

[...Array(5).keys()];
 => [0, 1, 2, 3, 4]

Character iteration

String.fromCharCode(...[...Array('D'.charCodeAt(0) - 'A'.charCodeAt(0) + 1).keys()].map(i => i + 'A'.charCodeAt(0)));
 => "ABCD"

Iteration

for (const x of Array(5).keys()) {
  console.log(x, String.fromCharCode('A'.charCodeAt(0) + x));
}
 => 0,"A" 1,"B" 2,"C" 3,"D" 4,"E"

As functions

function range(size, startAt = 0) {
    return [...Array(size).keys()].map(i => i + startAt);
}

function characterRange(startChar, endChar) {
    return String.fromCharCode(...range(endChar.charCodeAt(0) -
            startChar.charCodeAt(0), startChar.charCodeAt(0)))
}

As typed functions

function range(size:number, startAt:number = 0):ReadonlyArray<number> {
    return [...Array(size).keys()].map(i => i + startAt);
}

function characterRange(startChar:string, endChar:string):ReadonlyArray<string> {
    return String.fromCharCode(...range(endChar.charCodeAt(0) -
            startChar.charCodeAt(0), startChar.charCodeAt(0)))
}

lodash.js _.range() function

_.range(10);
 => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
_.range(1, 11);
 => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
_.range(0, 30, 5);
 => [0, 5, 10, 15, 20, 25]
_.range(0, -10, -1);
 => [0, -1, -2, -3, -4, -5, -6, -7, -8, -9]
String.fromCharCode(..._.range('A'.charCodeAt(0), 'D'.charCodeAt(0) + 1));
 => "ABCD"

Old non es6 browsers without a library:

Array.apply(null, Array(5)).map(function (_, i) {return i;});
 => [0, 1, 2, 3, 4]

console.log([...Array(5).keys()]);

(ES6 credit to nils petersohn and other commenters)

Answer 2

For numbers you can use ES6 Array.from(), which works in everything these days except IE:

Shorter version:

Array.from({length: 20}, (x, i) => i);

Longer version:

Array.from(new Array(20), (x, i) => i);​​​​​​

which creates an array from 0 to 19 inclusive. This can be further shortened to one of these forms:

Array.from(Array(20).keys());
// or
[...Array(20).keys()];

Lower and upper bounds can be specified too, for example:

Array.from(new Array(20), (x, i) => i + *lowerBound*);

An article describing this in more detail: http://www.2ality.com/2014/05/es6-array-methods.html

Answer 3

My new favorite form (ES2015)

Array(10).fill(1).map((x, y) => x + y)

And if you need a function with a step param:

const range = (start, stop, step = 1) =>
  Array(Math.ceil((stop - start) / step)).fill(start).map((x, y) => x + y * step)

Answer 4

Here's my 2 cents:

function range(start, end) {
  return Array.apply(0, Array(end - 1))
    .map((element, index) => index + start);
}

Answer 5

It works for characters and numbers, going forwards or backwards with an optional step.

var range = function(start, end, step) {
    var range = [];
    var typeofStart = typeof start;
    var typeofEnd = typeof end;

    if (step === 0) {
        throw TypeError("Step cannot be zero.");
    }

    if (typeofStart == "undefined" || typeofEnd == "undefined") {
        throw TypeError("Must pass start and end arguments.");
    } else if (typeofStart != typeofEnd) {
        throw TypeError("Start and end arguments must be of same type.");
    }

    typeof step == "undefined" && (step = 1);

    if (end < start) {
        step = -step;
    }

    if (typeofStart == "number") {

        while (step > 0 ? end >= start : end <= start) {
            range.push(start);
            start += step;
        }

    } else if (typeofStart == "string") {

        if (start.length != 1 || end.length != 1) {
            throw TypeError("Only strings with one character are supported.");
        }

        start = start.charCodeAt(0);
        end = end.charCodeAt(0);

        while (step > 0 ? end >= start : end <= start) {
            range.push(String.fromCharCode(start));
            start += step;
        }

    } else {
        throw TypeError("Only string and number types are supported");
    }

    return range;

}

jsFiddle.

If augmenting native types is your thing, then assign it to Array.range.

var range = function(start, end, step) {
    var range = [];
    var typeofStart = typeof start;
    var typeofEnd = typeof end;

    if (step === 0) {
        throw TypeError("Step cannot be zero.");
    }

    if (typeofStart == "undefined" || typeofEnd == "undefined") {
        throw TypeError("Must pass start and end arguments.");
    } else if (typeofStart != typeofEnd) {
        throw TypeError("Start and end arguments must be of same type.");
    }

    typeof step == "undefined" && (step = 1);

    if (end < start) {
        step = -step;
    }

    if (typeofStart == "number") {

        while (step > 0 ? end >= start : end <= start) {
            range.push(start);
            start += step;
        }

    } else if (typeofStart == "string") {

        if (start.length != 1 || end.length != 1) {
            throw TypeError("Only strings with one character are supported.");
        }

        start = start.charCodeAt(0);
        end = end.charCodeAt(0);

        while (step > 0 ? end >= start : end <= start) {
            range.push(String.fromCharCode(start));
            start += step;
        }

    } else {
        throw TypeError("Only string and number types are supported");
    }

    return range;

}

console.log(range("A", "Z", 1));
console.log(range("Z", "A", 1));
console.log(range("A", "Z", 3));


console.log(range(0, 25, 1));

console.log(range(0, 25, 5));
console.log(range(20, 5, 5));

Answer 6

Simple range function:

function range(start, stop, step) {
    var a = [start], b = start;
    while (b < stop) {
        a.push(b += step || 1);
    }
    return a;
}

---

To incorporate the BigInt data type some check can be included, ensuring that all variables are same typeof start:

function range(start, stop, step) {
    var a = [start], b = start;
    if (typeof start == 'bigint') {
        stop = BigInt(stop)
        step = step? BigInt(step): 1n;
    } else
        step = step || 1;
    while (b < stop) {
        a.push(b += step);
    }
    return a;
}

---

To remove values higher than defined by stop e.g. range(0,5,2) will include 6, which shouldn't be.

function range(start, stop, step) {
    var a = [start], b = start;
    while (b < stop) {
        a.push(b += step || 1);
    }
    return (b > stop) ? a.slice(0,-1) : a;
}

Answer 7

OK, in JavaScript we don't have a range() function like PHP, so we need to create the function which is quite easy thing, I write couple of one-line functions for you and separate them for Numbers and Alphabets as below:

for Numbers:

function numberRange (start, end) {
  return new Array(end - start).fill().map((d, i) => i + start);
}

and call it like:

numberRange(5, 10); //[5, 6, 7, 8, 9]

for Alphabets:

function alphabetRange (start, end) {
  return new Array(end.charCodeAt(0) - start.charCodeAt(0)).fill().map((d, i) => String.fromCharCode(i + start.charCodeAt(0)));
}

and call it like:

alphabetRange('c', 'h'); //["c", "d", "e", "f", "g"]

Answer 8

Array.range = function(a, b, step){
    var A = [];
    if(typeof a == 'number'){
        A[0] = a;
        step = step || 1;
        while(a+step <= b){
            A[A.length]= a+= step;
        }
    }
    else {
        var s = 'abcdefghijklmnopqrstuvwxyz';
        if(a === a.toUpperCase()){
            b = b.toUpperCase();
            s = s.toUpperCase();
        }
        s = s.substring(s.indexOf(a), s.indexOf(b)+ 1);
        A = s.split('');        
    }
    return A;
}
    
    
Array.range(0,10);
// [0,1,2,3,4,5,6,7,8,9,10]
    
Array.range(-100,100,20);
// [-100,-80,-60,-40,-20,0,20,40,60,80,100]
    
Array.range('A','F');
// ['A','B','C','D','E','F')
    
Array.range('m','r');
// ['m','n','o','p','q','r']

Answer 9

Handy function to do the trick, run the code snippet below

function range(start, end, step, offset) {
  
  var len = (Math.abs(end - start) + ((offset || 0) * 2)) / (step || 1) + 1;
  var direction = start < end ? 1 : -1;
  var startingPoint = start - (direction * (offset || 0));
  var stepSize = direction * (step || 1);
  
  return Array(len).fill(0).map(function(_, index) {
    return startingPoint + (stepSize * index);
  });
  
}

console.log('range(1, 5)=> ' + range(1, 5));
console.log('range(5, 1)=> ' + range(5, 1));
console.log('range(5, 5)=> ' + range(5, 5));
console.log('range(-5, 5)=> ' + range(-5, 5));
console.log('range(-10, 5, 5)=> ' + range(-10, 5, 5));
console.log('range(1, 5, 1, 2)=> ' + range(1, 5, 1, 2));

here is how to use it

range (Start, End, Step=1, Offset=0);

• inclusive - forward range(5,10) // [5, 6, 7, 8, 9, 10]
• inclusive - backward range(10,5) // [10, 9, 8, 7, 6, 5]
• step - backward range(10,2,2) // [10, 8, 6, 4, 2]
• exclusive - forward range(5,10,0,-1) // [6, 7, 8, 9] not 5,10 themselves
• offset - expand range(5,10,0,1) // [4, 5, 6, 7, 8, 9, 10, 11]
• offset - shrink range(5,10,0,-2) // [7, 8]
• step - expand range(10,0,2,2) // [12, 10, 8, 6, 4, 2, 0, -2]

hope you find it useful.

---

And here is how it works.

Basically I'm first calculating the length of the resulting array and create a zero filled array to that length, then fill it with the needed values

• (step || 1) => And others like this means use the value of step and if it was not provided use 1 instead
• We start by calculating the length of the result array using (Math.abs(end - start) + ((offset || 0) * 2)) / (step || 1) + 1) to put it simpler (difference* offset in both direction/step)
• After getting the length, then we create an empty array with initialized values using new Array(length).fill(0); check here
• Now we have an array [0,0,0,..] to the length we want. We map over it and return a new array with the values we need by using Array.map(function() {})
• var direction = start < end ? 1 : 0; Obviously if start is not smaller than the end we need to move backward. I mean going from 0 to 5 or vice versa
• On every iteration, startingPoint + stepSize * index will gives us the value we need

Answer 10

var range = (l,r) => new Array(r - l).fill().map((_,k) => k + l);

Answer 11

--- UPDATE (Thanks to @lokhmakov for simplification) ---

Another version using ES6 generators ( see great Paolo Moretti answer with ES6 generators ):

const RANGE = (x,y) => Array.from((function*(){
  while (x <= y) yield x++;
})());

console.log(RANGE(3,7));  // [ 3, 4, 5, 6, 7 ]

Or, if we only need iterable, then:

const RANGE_ITER = (x,y) => (function*(){
  while (x <= y) yield x++;
})();

for (let n of RANGE_ITER(3,7)){
  console.log(n);
}

// 3
// 4
// 5
// 6
// 7

--- ORGINAL code was: ---

const RANGE = (a,b) => Array.from((function*(x,y){
  while (x <= y) yield x++;
})(a,b));

and

const RANGE_ITER = (a,b) => (function*(x,y){
  while (x <= y) yield x++;
})(a,b);

Answer 12

https://stackoverflow.com/a/49577331/8784402

With Delta/Step

[...Array(N)].map((_, i) => from + i * step);

Examples and other alternatives

[...Array(10)].map((_, i) => 4 + i * 2);
//=> [4, 6, 8, 10, 12, 14, 16, 18, 20, 22]

Array.from(Array(10)).map((_, i) => 4 + i * 2);
//=> [4, 6, 8, 10, 12, 14, 16, 18, 20, 22]

Array.from(Array(10).keys()).map(i => 4 + i * 2);
//=> [4, 6, 8, 10, 12, 14, 16, 18, 20, 22]

[...Array(10).keys()].map(i => 4 + i * -2);
//=> [4, 2, 0, -2, -4, -6, -8, -10, -12, -14]

Array(10).fill(0).map((_, i) => 4 + i * 2);
//=> [4, 6, 8, 10, 12, 14, 16, 18, 20, 22]

Array(10).fill().map((_, i) => 4 + i * -2);
//=> [4, 2, 0, -2, -4, -6, -8, -10, -12, -14]

const range = (from, to, step) =>
  [...Array(Math.floor((to - from) / step) + 1)].map((_, i) => from + i * step);

range(0, 9, 2);
//=> [0, 2, 4, 6, 8]

// can also assign range function as static method in Array class (but not recommended )
Array.range = (from, to, step) =>
  [...Array(Math.floor((to - from) / step) + 1)].map((_, i) => from + i * step);

Array.range(2, 10, 2);
//=> [2, 4, 6, 8, 10]

Array.range(0, 10, 1);
//=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Array.range(2, 10, -1);
//=> []

Array.range(3, 0, -1);
//=> [3, 2, 1, 0]

class Range {
  constructor(total = 0, step = 1, from = 0) {
    this[Symbol.iterator] = function* () {
      for (let i = 0; i < total; yield from + i++ * step) {}
    };
  }
}

[...new Range(5)]; // Five Elements
//=> [0, 1, 2, 3, 4]
[...new Range(5, 2)]; // Five Elements With Step 2
//=> [0, 2, 4, 6, 8]
[...new Range(5, -2, 10)]; // Five Elements With Step -2 From 10
//=>[10, 8, 6, 4, 2]
[...new Range(5, -2, -10)]; // Five Elements With Step -2 From -10
//=> [-10, -12, -14, -16, -18]

// Also works with for..of loop
for (i of new Range(5, -2, 10)) console.log(i);
// 10 8 6 4 2

const Range = function* (total = 0, step = 1, from = 0) {
  for (let i = 0; i < total; yield from + i++ * step) {}
};

Array.from(Range(5, -2, -10));
//=> [-10, -12, -14, -16, -18]

[...Range(5, -2, -10)]; // Five Elements With Step -2 From -10
//=> [-10, -12, -14, -16, -18]

// Also works with for..of loop
for (i of Range(5, -2, 10)) console.log(i);
// 10 8 6 4 2

// Lazy loaded way
const number0toInf = Range(Infinity);
number0toInf.next().value;
//=> 0
number0toInf.next().value;
//=> 1
// ...

From-To with steps/delta

class Range2 {
  constructor(to = 0, step = 1, from = 0) {
    this[Symbol.iterator] = function* () {
      let i = 0,
        length = Math.floor((to - from) / step) + 1;
      while (i < length) yield from + i++ * step;
    };
  }
}
[...new Range2(5)]; // First 5 Whole Numbers
//=> [0, 1, 2, 3, 4, 5]

[...new Range2(5, 2)]; // From 0 to 5 with step 2
//=> [0, 2, 4]

[...new Range2(5, -2, 10)]; // From 10 to 5 with step -2
//=> [10, 8, 6]

const Range2 = function* (to = 0, step = 1, from = 0) {
  let i = 0,
    length = Math.floor((to - from) / step) + 1;
  while (i < length) yield from + i++ * step;
};

[...Range2(5, -2, 10)]; // From 10 to 5 with step -2
//=> [10, 8, 6]

let even4to10 = Range2(10, 2, 4);
even4to10.next().value;
//=> 4
even4to10.next().value;
//=> 6
even4to10.next().value;
//=> 8
even4to10.next().value;
//=> 10
even4to10.next().value;
//=> undefined

For Typescript

class _Array<T> extends Array<T> {
  static range(from: number, to: number, step: number): number[] {
    return Array.from(Array(Math.floor((to - from) / step) + 1)).map(
      (v, k) => from + k * step
    );
  }
}
_Array.range(0, 9, 1);

https://stackoverflow.com/a/64599169/8784402

Generate Character List with one-liner

const charList = (a,z,d=1)=>(a=a.charCodeAt(),z=z.charCodeAt(),[...Array(Math.floor((z-a)/d)+1)].map((_,i)=>String.fromCharCode(a+i*d)));

console.log("from A to G", charList('A', 'G'));
console.log("from A to Z with step/delta of 2", charList('A', 'Z', 2));
console.log("reverse order from Z to P", charList('Z', 'P', -1));
console.log("from 0 to 5", charList('0', '5', 1));
console.log("from 9 to 5", charList('9', '5', -1));
console.log("from 0 to 8 with step 2", charList('0', '8', 2));
console.log("from α to ω", charList('α', 'ω'));
console.log("Hindi characters from क to ह", charList('क', 'ह'));
console.log("Russian characters from А to Я", charList('А', 'Я'));

const charList = (p: string, q: string, d = 1) => {
  const a = p.charCodeAt(0),
    z = q.charCodeAt(0);
  return [...Array(Math.floor((z - a) / d) + 1)].map((_, i) =>
    String.fromCharCode(a + i * d)
  );
};

Answer 13

Using Harmony spread operator and arrow functions:

var range = (start, end) => [...Array(end - start + 1)].map((_, i) => start + i);

Example:

range(10, 15);
[ 10, 11, 12, 13, 14, 15 ]

Answer 14

You can use lodash or Undescore.js range:

var range = require('lodash/range')
range(10)
// -> [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ]

---

Alternatively, if you only need a consecutive range of integers you can do something like:

Array.apply(undefined, { length: 10 }).map(Number.call, Number)
// -> [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ]

---

In ES6 range can be implemented with generators:

function* range(start=0, end=null, step=1) {
  if (end == null) {
    end = start;
    start = 0;
  }

  for (let i=start; i < end; i+=step) {
    yield i;
  }
}

This implementation saves memory when iterating large sequences, because it doesn't have to materialize all values into an array:

for (let i of range(1, oneZillion)) {
  console.log(i);
}

Answer 15

Did some research on some various Range Functions. Checkout the jsperf comparison of the different ways to do these functions. Certainly not a perfect or exhaustive list, but should help :)

The Winner is...

function range(lowEnd,highEnd){
    var arr = [],
    c = highEnd - lowEnd + 1;
    while ( c-- ) {
        arr[c] = highEnd--
    }
    return arr;
}
range(0,31);

Technically its not the fastest on firefox, but crazy speed difference (imho) on chrome makes up for it.

Also interesting observation is how much faster chrome is with these array functions than firefox. Chrome is at least 4 or 5 times faster.

Answer 16

The standard Javascript doesn't have a built-in function to generate ranges. Several javascript frameworks add support for such features, or as others have pointed out you can always roll your own.

If you'd like to double-check, the definitive resource is the ECMA-262 Standard.

Answer 17

This may not be the best way. But if you are looking to get a range of numbers in a single line of code. For example 10 - 50

Array(40).fill(undefined).map((n, i) => i + 10)

Where 40 is (end - start) and 10 is the start. This should return [10, 11, ..., 50]

Answer 18

range(start,end,step): With ES6 Iterators

You only ask for an upper and lower bounds. Here we create one with a step too.

You can easily create range() generator function which can function as an iterator. This means you don't have to pre-generate the entire array.

function * range ( start, end, step = 1 ) {
  let state = start;
  while ( state < end ) {
    yield state;
    state += step;
  }
  return;
};

Now you may want to create something that pre-generates the array from the iterator and returns a list. This is useful for functions that accept an array. For this we can use Array.from()

const generate_array = (start,end,step) =>
  Array.from( range(start,end,step) );

Now you can generate a static array easily,

const array1 = generate_array(1,10,2);
const array1 = generate_array(1,7);

But when something desires an iterator (or gives you the option to use an iterator) you can easily create one too.

for ( const i of range(1, Number.MAX_SAFE_INTEGER, 7) ) {
  console.log(i)
}

Special Notes

• If you use Ramda, they have their own R.range as does Lodash

Answer 19

An interesting challenge would be to write the shortest function to do this. Recursion to the rescue!

function r(a,b){return a>b?[]:[a].concat(r(++a,b))}

Tends to be slow on large ranges, but luckily quantum computers are just around the corner.

An added bonus is that it's obfuscatory. Because we all know how important it is to hide our code from prying eyes.

To truly and utterly obfuscate the function, do this:

function r(a,b){return (a<b?[a,b].concat(r(++a,--b)):a>b?[]:[a]).sort(function(a,b){return a-b})}

Answer 20

My personal favorite:

const range = (start, end) => new Array(end-start+1).fill().map((el, ind) => ind + start);

Answer 21

I would code something like this:

function range(start, end) {
    return Array(end-start).join(0).split(0).map(function(val, id) {return id+start});
}  

range(-4,2);
// [-4,-3,-2,-1,0,1]

range(3,9);
// [3,4,5,6,7,8]

It behaves similarly to Python range:

>>> range(-4,2)
[-4, -3, -2, -1, 0, 1]

Answer 22

A rather minimalistic implementation that heavily employs ES6 can be created as follows, drawing particular attention to the Array.from() static method:

const getRange = (start, stop) => Array.from(
  new Array((stop - start) + 1),
  (_, i) => i + start
);

Answer 23

Though this is not from PHP, but an imitation of range from Python.

function range(start, end) {
    var total = [];

    if (!end) {
        end = start;
        start = 0;
    }

    for (var i = start; i < end; i += 1) {
        total.push(i);
    }

    return total;
}

console.log(range(10)); // [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] 
console.log(range(0, 10)); // [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
console.log(range(5, 10)); // [5, 6, 7, 8, 9] 

Answer 24

This one works also in reverse.

const range = ( a , b ) => Array.from( new Array( b > a ? b - a : a - b ), ( x, i ) => b > a ? i + a : a - i );

range( -3, 2 ); // [ -3, -2, -1, 0, 1 ]
range( 1, -4 ); // [ 1, 0, -1, -2, -3 ]

Answer 25

As far as generating a numeric array for a given range, I use this:

function range(start, stop)
{
    var array = [];

    var length = stop - start; 

    for (var i = 0; i <= length; i++) { 
        array[i] = start;
        start++;
    }

    return array;
}

console.log(range(1, 7));  // [1,2,3,4,5,6,7]
console.log(range(5, 10)); // [5,6,7,8,9,10]
console.log(range(-2, 3)); // [-2,-1,0,1,2,3]

Obviously, it won't work for alphabetical arrays.

Answer 26

You can create your own es6 range version

const range = (min, max) => {
  const arr = Array(max - min + 1)
    .fill(0)
    .map((_, i) => i + min);
  return arr;
}

console.log(range(0,5));

console.log(range(2,8))

Answer 27

You can use following one-liner to keep things short and simple

var start = 4;
var end = 20;
console.log(Array(end - start + 1).fill(start).map((x, y) => x + y));

Answer 28

Not implemented yet!

Using the new Number.range proposal (stage 1):

[...Number.range(1, 10)]
//=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Answer 29

Use this. It creates an array with given amount of values (undefined), in the following example there are 100 indexes, but it is not relevant as here you need only the keys. It uses in the array, 100 + 1, because the arrays are always 0 index based. So if it's given 100 values to generate, the index starts from 0; hence the last value is always 99 not 100.

range(2, 100);

function range(start, end) {
    console.log([...Array(end + 1).keys()].filter(value => end >= value && start <= value ));
}

Answer 30

d3 also has a built-in range function. See https://github.com/mbostock/d3/wiki/Arrays#d3_range:

d3.range([start, ]stop[, step])

Generates an array containing an arithmetic progression, similar to the Python built-in range. This method is often used to iterate over a sequence of numeric or integer values, such as the indexes into an array. Unlike the Python version, the arguments are not required to be integers, though the results are more predictable if they are due to floating point precision. If step is omitted, it defaults to 1.

Example:

d3.range(10)
// returns [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]