Some Javascript interview questions.


1. What should be the output of the following code snippet.


const arr = [1, 2, 3, 4];
for (var i = 0; i < arr.length; i++) {
  setTimeout(function() {
    console.log('Index: ' + i + ', element: ' + arr[i]);
  }, 4000);
}

 Output : 
Index: 4 ,  element: undefined

Explanation :
Actually the setTimeout function will create a closure function which have access to the upper local variable i . So once the for loop gets executed the setTimeout function is get executed and the i value goes up . So within this 1 sec the i value goes upto 4 and the arr[4] value would be undefined .

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