Why js throws an error, but at the same time quietly displays the necessary data?

Question

JavaScript

var dat = JSON.parse(datadel);
  var lbls = new Array();
  for (var i = 0; i<= dat.length; i++) {
    lbls[i] = dat[i]['name'];
    console.log(lbls[i]);
  }

During the execution of the code, it is executed, but it throws a TypeError error, which breaks the further execution of the code.

Answer 1

Because dat[dat.length] doesn't exist and you're trying to output it.