Nested For loop

JavaScript
1

Can any body explain me the code below ? How does inner for loop works for that problem.


var arr = [
  [1,2], [3,4], [5,6]
];
for (var i=0; i < arr.length; i++) {
  for (var j=0; j < arr[i].length; j++) {
    console.log(arr[i][j]);
  }
}
2

I’ve edited your post for readability. When you enter a code block into a forum post, please precede it with a separate line of three backticks and follow it with a separate line of three backticks to make easier to read.

See this post to find the backtick on your keyboard. The “preformatted text” tool in the editor (</>) will also add backticks around text.

Note: Backticks are not single quotes.

markdown_Forums

4

The first loop defines the value for variable ‘i’, and specifies to loop until ‘i’ is equal to the array length (loop through each array item):

The nested loop creates new variable ‘j’ and specifies to loop until ‘j’ is equal to the length of each nested array item (the array within the array):

The code then loops to log each item in the nested arrays to the console:

5

Dear Members,

Is there any website where I can understand my block of code step by step ?

6

I don’t know if it is step by step enough, but I really like this: http://pythontutor.com/javascript.html

1 Like
7

Yes exactly. I was asking for this.

Thank you.

8

@camperextraordinaire I m not getting this what is j < arr[i].length used for ??

have confusion in second loop, cannot understand the code there.

9

The j is used to loop over the elements of the sub-arrays

10

@TatTheFlame How nested loop works means if this condition fulfills for (var i=0; i < arr.length; i++) then it direct go to this loop for (var j=0; j < arr[i].length; j++) ?
and what is arr[i].length in it ?

literally it is blowing my head, hope this is normal for a newbie. :slight_smile:

11

Try looking at the nested for loops with this: http://pythontutor.com/javascript.html

If you don’t get it yet we can try again to explain it