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Discussion on: JavaScript Closures: A Simple Explanation.

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stereobooster •

You can mention binding as well. let has lexical scope binding (e.g. it binded inside for ), where is var has scope of function body:

function countdown(upto) {
  for (let i = 0; i < upto; i++) {
    setTimeout(() => console.log(i), 1000);
  }
};
countdown(5); // Output: 0 1 2 3 4

Or using bind:

function arrayOfNums(num) {
  var output = [];
  for (var i = 0; i < num; i++) {
    output.push((function(x) { return x; }).bind(null, i)); 
  }
  return output;
}
arr[0](); // Output: 0