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JavaScript JavaScript Loops, Arrays and Objects Tracking Multiple Items with Arrays Build a Quiz Challenge, Part 2 Solution

Posted by Carey Cooke
Carey Cooke
3,952 Points

In the loop for buildList(arr), where does the arr.length come from since it was never declared as a variable above?

In the function buldList(arr), the for loop is set to run as i < arr.length. However, arr was never set as a variable of any kind so how does the program know that it's an array or any other kind of variable?

for ( var i=0; i < arr.length; i +=1) { listHTML += '<li>' + arr[i] + '</li>'; }

I didn't include the entire function because this is the only par that confused me.

1 Answer

pi R
pi R
12,720 Points
pi R
pi R
12,720 Points

Hi ! arr is an argument of the function! so arr.length will be the length of the argument you pass to buildList(arr);

example : var arrayOne = [];

buildList(arrayOne) will do : for ( var i=0; i < arrayOne.length; i +=1) { listHTML += '' + arrayOne[i] + ''; }

Iain Simmons
Iain Simmons
Treehouse Moderator 32,305 Points

It's also important to note that arrays aren't the only types that have a length property. If a string was passed to this function, it would still work, but you would get a weird list of each character (including spaces and punctuation) in its own list item.