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Loop Over Array in Javascript [duplicate]

I'm using Google Chrome's Console window to try and figure out why I'm not able to loop over an array in javascript.

I have a javascript object called moveResult that looks like this:

enter image description here

I'm trying to loop over the MoveParts in javascript like this:

for (var movePart in moveResult.MoveParts) {     console.log(movePart.From); }; 

I always get undefined instead of the actual value. However, If I try to access the first item explicitly I get what I want, like this:

console.log(moveResult.MoveParts[0].From); 

The result of this is "b1".

Why isn't my loop working?

I've also tried a foreach:

moveResult.MoveParts.foreach(function (movePart) {     console.log(movePart.From); }; 
like image 474
PeteGO Avatar asked Dec 23 '14 18:12

PeteGO


Video Answer


1 Answers

I'm trying to loop over the MoveParts in javascript like this:

for (var movePart in moveResult.MoveParts) {     console.log(movePart.From); }; 

I always get undefined instead of the actual value.

Don't use for-in to loop through arrays, that's not what it's for. for-in is for looping through object properties. This answer shows various ways to loop through arrays.

The reason your for-in didn't work is that movePart is the key, not the actual entry, so if you were using an object (not an array!) you would have used moveResult.MoveParts[movePart].From.

Your forEach version only failed because:

  1. It's forEach, not foreach. Capitalization matters in JavaScript.

  2. You were missing the closing ) on the function call.

The answer linked above has full examples of forEach and others, but here's how yours should have looked:

    moveResult.MoveParts.forEach(function (movePart) {     // Capital E -----------^         console.log(movePart.From);     }); //   ^---- closing ) 
like image 74
T.J. Crowder Avatar answered Oct 04 '22 05:10

T.J. Crowder