What does "array.length -1" mean in JavaScript?

Question

I know how to use the JavaScript for loops to cycle through arrays for example, but I still didn't understand what the array.length -1 means, specifically the -1 part.

When using a for loop over an array we have something like this:

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

But I've seen also something like this, sometimes:

for (i = 0; i < array.length - 1; i++) {...}

In the second case, why there is the "-1" in the array.length and what does it do? Also why sometimes there is and sometimes isn't it shown?

Answer 1

If your array has 4 elements, for example

var elementOfArray = [7, 9, 0, 2]

and you want to reach those elements. In that case, you need to know that elementOfArray[i] represents element of your array and i is the index.

For that reason, if you add '-1' on your array length; you can see whole elements in your array like elementOfArray[0]---7, elementOfArray[1]---9, elementOfArray[2]---0, elementOfArray[3]---2. See! you took the whole number in the element.

If you do not subtract 1 of array length, you would take an error. Because there is no elementOfArray[4] that represents any element of your array.