How to coalesce an array in JavaScript/CoffeeScript?

Question

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

ideally coalesce should iterate over arguments, but it doesn't support reduce, and
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

Guffa · Accepted Answer · 2012-04-24 13:59:17Z

3

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

answered Apr 24, 2012 at 13:59

Guffa

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Comments

MrCADman · Accepted Answer · 2023-03-16 18:57:15Z

0

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 );

answered Mar 16, 2023 at 18:57

MrCADman

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