CODEWITHSUNDEEP
javascriptnullcoffeescriptnull-coalescing-operator
l0b0
l0b0

Reputation: 58988

How to coalesce an array in JavaScript/CoffeeScript?

Coalescing a static set of items is easy:

var finalValue = configValue || "default"; # JavaScript
finalValue = configValue ? "default" # CoffeeScript

But is there a simple way to coalesce an array of unknown length? The simplest I could come up with was this (CoffeeScript):

coalesce = (args) -> args.reduce (arg) -> arg if arg?
coalesce [1, 2] # Prints 1

That's fine for simple lists, but

  1. ideally coalesce should iterate over arguments, but it doesn't support reduce, and
  2. if the array contains functions, you might want to return their return value rather than the functions themselves (this is my use case).

Based on Guffa's solution, here's a CoffeeScript version:

coalesce = (args) -> args[0]() ? coalesce args[1..]

Test in coffee:

fun1 = ->
  console.log 1
  null
fun2 = ->
  console.log 2
  2
fun3 = ->
  console.log 3
  3
coalesce [fun1, fun2, fun3]

Prints

1 # Log
2 # Log
2 # Return value

Upvotes: 1

Views: 5478

Answers (2)

MrCADman
MrCADman

Reputation: 109

This function works perfectly for me:

function coalesce(...param){
    if (param.length == 0) return null;
      return param.find(a => a !== null);
}

let value = coalesce(null, null, 1,2,3,4);
console.log('value = ', value );

Upvotes: 0

Guffa
Guffa

Reputation: 700880

You can do like this:

function coalesce(arr) {
  if (arr.length == 0) return null;
  var v = arr[0];
  v = (typeof v == "function" ? v() : v);
  return v | coalesce(arr.slice(1));
}

Example:

var finalValue = coalesce([ null, null, function(){ return null; }, 5 ]);
// finalValue is now 5

Upvotes: 3

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