Why is the score correctly increasing

Question

Consider this simple example:

var count = 0;
for (var i = 0; i < 4; i++ ) {
    setTimeout(function() {
      console.log(i, count++);
    }, i * 200);
}

which displays the following

4 0
4 1
4 2
4 3

I would suggest that it ialways resolves to 4, because the setTimeout callback closes on variable I, but I cannot figure out why the same is not true for count?

var count = 0;
for (var i = 0; i < 4; i++ ) {
  setTimeout(function() {
    console.log(i, count++);
  }, i * 2000 );
}

Run code

Answer 1

The variable is iincremented by your loop forand ends with a value 4until any of the timeout handlers are started. On the other hand, the variable countonly increases in timeout handlers. When the first timeout handler fires, it countstill will 0.

Answer 2

: " , , - ".

, - i . , i

count ; .

for (var i = 0; i < 4; i++) {
    doSomething(i);
};
function doSomething(i) {
    setTimeout(function() {
        console.log(i);
    }, i * 2000);
};