Forgot to comment my code. Why does this work?

JavaScript
1

Here are the instructions:

We’ll be rebuilding the native .join array method. The join function should work as follows:

// If the input is empty, return an empty string
join([]) // ''

// If there is no separator, separate by commas
join([ 'a', 'b', 'c' ]) // 'a,b,c'

// If there is a separator, separate by that string
join([ 'a', 'b', 'c' ], '-') // 'a-b-c'

// If there is only one item, return just that item
join([ 'a' ], '---') // 'a'

I’m just a bit confused on this line:

if (separator && array[i] !== array[array.length-1])

Here is my code:

function join (array, separator) {
    let str = '';
    for (let i = 0; i < array.length; i++) {
      str += array[i];
      if (separator && array[i] !== array[array.length-1]) {
        str += separator;
      } else if (array[i] !== array[array.length-1]) {
        str += ',';
      }
    }
    return str;
  }
2

Roughly in English, that means, “if there is a separator, and the ith element in the array is not the last element, do the following…”

3

Thanks man. Appreciate it.

5

You are insane at this. Truly. I can only hope at some point I get that good.

6

Also, if you find time, could you comment that regular expression using RegExp? I’m trying to learn Regex as it seems to be the best way to solve a lot of things that I tend to complicate.