I didn't know I didn't know the answer when my friend showed me a simple piece of JavaScript code and asked me what would happen.

He said this caused a bug in a project he was working on and it took him hours to debug. Since I knew arrays in JavaScript are objects. And objects are only equal when they refer to the same thing in memory. If you do it as shown in ex. {2}, the result will certainly be true, because x and y indeed refer to the same thing.

In ex. {1}, a and b are defined differently. And I felt very clever when I correctly said the code on line 🕶 will produce a false. But —

“If we compare a.valueOf() == b.valueOf(), the result will surely be true!” ⋯

This is essentially how you emulate the way Python's zip() function works using JavaScript.

What makes this possible is the fact that JavaScript array methods — map(), forEach() and even filter() — take up to three arguments (element, index, array) while they iterate through the array.

In which element is the element that the iterator points to at each step, index is the index of this item in the original array. And it's worth noting the third argument is the original array.

Since map() method of the JavaScript array is more flexible than zip(), we can do more stuff to the iterated item or the array. But if you want to do anything with array, remember the original array changes accordingly. In this case, a: ⋯