variable i is not passed into a function in a loop in JavaScript

Question

I understand there is no block level scope for var i ; however, in the following code, d.push(); is executed after the initialisation of i, why i here remains undefined?

var d = [];
for (var i = 0; i < 3; i++) {
     d.push(function(i) {
        console.log('iterator: ' + i);
    });
}
d[0]();//undefined

Any thoughts will be appreciated

Answer 1

You can push an argument-bound version of the anonymous function by using .bind() thereby ensuring the value of the first argument.

var d = [];
for (var i = 0; i < 3; i++) {
    d.push((function(i) {
        console.log('iterator: ' + i);
    }).bind(this, i));
}
d[0](); // iterator: 0
d[1](); // iterator: 1
d[2](); // iterator: 2