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JavaScript JavaScript Loops, Arrays and Objects Tracking Data Using Objects Using `for in` to Loop Through an Object's Properties

Why in for in loop don't we use var?

Hi guys, I don't understand why in the exampla Dave shows that the typical for in loop works in this way for (var key in student) { }

and in the example he uses the command without var for (prop in person { }

Why doesn't he uses the word var??

Thanks to all

2 Answers

Jacob Bergdahl
Jacob Bergdahl
29,118 Points

In Javascript, you can choose to not use the var keyword in a for in loop. However, it is usually best to use the var keyword and NOT do like the teacher did here. If you don't write var before the variable name, you create a global variable, which may not be preferable, as it could break the code. If you don't know what a global variable is, don't worry about it just yet. Just remember to use the var keyword, as it is indeed usually the best way to write a for in loop.

Jason Anders
Jason Anders
Treehouse Moderator 145,855 Points

Hey Luca,

Both variants will work, and I found a great forum thread that explains the different ways very nicely.

Hope that helps. :)


I had the same question as OP, and found this link really helpful! Thanks for posting it.