Getting variable is indefined error inside a for loop

Question

Here is my JavaScript code:

var all_videos = document.querySelectorAll(".video-feed-item-wrapper");
var all_urls = [];
console.log(all_videos.length);
for(i = 0; i <= all_videos.length; i++) {
  all_urls.push(all_videos[i].getAttribute('href'));
}
console.log(all_urls);

It gives me the error all_videos[i] is undefined. Why is it undefined?

Thanks.

Here i becomes a global variable use let,var here for(i = 0; i <= all_videos.length; i++) { — brk
– brk, Commented May 5, 2020 at 16:38
Is there anything in all_videos in that console.log call ? — cronoklee
– cronoklee, Commented May 5, 2020 at 16:39

brk · Accepted Answer · 2020-05-05 16:43:58Z

2

Two issues here , first i becomes a global variable and instead i <= all_videos.length use only i < all_videos.length. It is undefined because i trying the access the element which is not available. The element is not available because index starts from 0

for(i = 0; i < all_videos.length; i++) {
  all_urls.push(all_videos[i].getAttribute('href'));
}

edited May 5, 2020 at 16:43

answered May 5, 2020 at 16:40

brk

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2 Comments

Real Noob Over a year ago

Just removing the the = from <= resolved the error. :) Are there any cases where keeping i global would have become a problem?

brk Over a year ago

@RealNoob Global variable creates risk in javascript since it can be accessed by other function. For example if in other loop if you use same i then there will be a collision . So scoping variable is important

Michał Z. · Accepted Answer · 2020-05-05 16:42:34Z

1

For loop should iterate from 0 to length-1

Condition in for loop should be i < all_videos.length instead of i <= all_videos.length

The correct line should be:

for(i = 0; i < all_videos.length; i++) {

answered May 5, 2020 at 16:42

Michał Z.

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