Create an array of characters from specified range

Question

I read some code where someone did this in Ruby:

puts ('A'..'Z').to_a.join(',') 

output:

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 

Is there something in Javascript that will allow this to be done just as easy? if not, is there Node module that allows for something similar?

Answer 1

If you're using ES6, you can generate a sequence using Array.from() by passing in an array-like object for the length of the range, and a map function as a second argument to convert the array key of each item in the range into a character using String.fromCharCode():

Array.from({ length: 26 }, (_, i) => String.fromCharCode('A'.charCodeAt(0) + i)); 

You can also use the Array constructor (note: ES6 allows constructors to be invoked either with a function call or with the new operator) to initialize an array of the desired default length, fill it using Array.fill(), then map through it:

Array(26).fill().map((_, i) => String.fromCharCode('A'.charCodeAt(0) + i)); 

The same can be accomplished with the spread operator:

[...Array(26)].map((_, i) => String.fromCharCode('A'.charCodeAt(0) + i)); 

The above three examples will return an array with characters from A to Z. For custom ranges, you can adjust the length and starting character.

For browsers that don't support ES6, you can use babel-polyfill or core-js polyfill (core-js/fn/array/from).

If you're targeting ES5, I would recommend the Array.apply solution by @wires which is very similar to this one.

Lastly, Underscore/Lodash and Ramda have a range() function:

_.range('A'.charCodeAt(0), 'Z'.charCodeAt(0) + 1).map(i => String.fromCharCode(i)); 

Answer 2

Javascript doesn't have that functionality natively. Below you find some examples of how it could be solved:

Normal function, any characters from the base plane (no checking for surrogate pairs)

function range(start,stop) {   var result=[];   for (var idx=start.charCodeAt(0),end=stop.charCodeAt(0); idx <=end; ++idx){     result.push(String.fromCharCode(idx));   }   return result; };  range('A','Z').join(); 

The same as above, but as a function added to the array prototype, and therefore available to all arrays:

Array.prototype.add_range = function(start,stop) {   for (var idx=start.charCodeAt(0),end=stop.charCodeAt(0); idx <=end; ++idx){     this.push(String.fromCharCode(idx));   }   return this; };  [].add_range('A','Z').join(); 

A range from preselected characters. Is faster than the functions above, and let you use alphanum_range('A','z') to mean A-Z and a-z:

var alphanum_range = (function() {   var data = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789'.split('');   return function (start,stop) {     start = data.indexOf(start);     stop = data.indexOf(stop);     return (!~start || !~stop) ? null : data.slice(start,stop+1);   }; })();  alphanum_range('A','Z').join(); 

Or any character from the ascii range. By using a cached array, it is faster than the functions that build the array every time.

var ascii_range = (function() {   var data = [];   while (data.length < 128) data.push(String.fromCharCode(data.length));   return function (start,stop) {     start = start.charCodeAt(0);     stop = stop.charCodeAt(0);     return (start < 0 || start > 127 || stop < 0 || stop > 127) ? null : data.slice(start,stop+1);   }; })();  ascii_range('A','Z').join();