Using forEach vs for(var key) with an associative array

Question

I just want to know why forEach doesn't work on an associative array:

var array =[];
array['W'] = 0;
array['S'] = 1;

// This doesn't work
console.log(array);
array.forEach(function(item){
console.log(item);
});

// This does
for(var key in array){
console.log(array[key]);
}

You are using an array like an object. Arrays are objects, but they're not used like that. var array = []; should be var object = {};, then it will become clear. — ibrahim mahrir
– ibrahim mahrir, Commented Dec 15, 2017 at 0:15
if i change array to var array ={}; it'd throw a not a function error on the forEach function as it only runs on arrays. — Naguib Ihab
– Naguib Ihab, Commented Dec 15, 2017 at 0:20

zerkms · Accepted Answer · 2017-12-15 00:20:43Z

3

Array.prototype.forEach is defined by the standard to iterate over index members.

for-in enumerates all object properties.

So in short, the answer to your "why" question is: because the standard says so.

answered Dec 15, 2017 at 0:20

zerkms

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Comments

SimpleJ · Accepted Answer · 2017-12-15 00:18:28Z

1

Probably because array.length evaluates to 0. You could use Object.values(array).forEach to iterate over the actual values of the array.

answered Dec 15, 2017 at 0:18

SimpleJ

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2 Comments

Naguib Ihab Over a year ago

You're right this works: Object.values(array).forEach(function(item){ console.log('2',item); });

ibrahim mahrir Over a year ago

@NaguibIhab If you are using Object.values then you might as well change var array = [] to var object = {}.

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