如何将事件监听器添加到html集合中的每个元素？

Question

function eventAdded(i) {
  console.log(inputs[i]);
}
var inputs = document.querySelectorAll('.js-capture__input input');
for (i = 0; i <= inputs.length; i++) {
  console.log(inputs[i]);
  inputs[i].addEventListener('change', eventAdded);
}

I am managing to log each inputs[i] to the console. inputs[i] exists. But I am getting Uncaught TypeError: Cannot read property 'addEventListener' of undefined

How is this not defined if I can log each one to the console? Can someone please explain like I'm 5?

Answer 1

Like @CertainPerformance said, your error is having i <= inputs.length instead of i < inputs.length .

The difference is that in the first case, you are going outside the boundaries of the array.

For example, if you have an array of 5 elements (remember arrays are 0-based):

0
1
2
3
4

When you check using i <= inputs.length , this is what's happening:

0 <= 5: true
1 <= 5: true
2 <= 5: true
3 <= 5: true
4 <= 5: true
5 <= 5: true
6 <= 5: false

So instead of iterating 5 times, you are iterating 6 times. The last one ( i=5 ), is not within the array boundaries (its upper bound is 4 ).

 function eventAdded(i) { console.log(inputs[i]); } var inputs = document.querySelectorAll('.js-capture__input input'); for (var i = 0; i < inputs.length; i++) { console.log(inputs[i]); inputs[i].addEventListener('change', eventAdded); }