CODEWITHSUNDEEP
javascript
Keith M
Keith M

Reputation: 461

Unexpected setTimeOut() function behavior in JavaScript

I came across this simple(or what I thought so) question on a Javascript MCQ Test:

After how much time will the following code execute entirely?

setTimeOut(console.log("hi"),1000);
setTimeOut(console.log("hi"),1000);
setTimeOut(console.log("hi"),1000);
setTimeOut(console.log("hi"),1000);
setTimeOut(console.log("hi"),1000);

Options
    A) 1 second
    B) 2 seconds
    C) 4 seconds
    D) 5 seconds

I answered as option D) 5 seconds since EACH line above will take 1000 milliseconds to execute i.e a total of 5000 milliseconds = 5 seconds

But in the results, it said that the actual answer is Option A) 1 second.

I executed those five lines in my console (altogether) and the entire code executed after 1 second like the answer said.

I don't understand the logic behind the right answer, and why my reasoning was wrong.

Upvotes: 1

Views: 1374

Answers (3)

Sythnet Partridge
Sythnet Partridge

Reputation: 51

Each call you make it running in it's own background thread (it's own unique operation), when you call setTimeout, you're telling JavaScript that you want to execute your code after 1 second has passed.

If you wanted to make this last 5 seconds you would do something along the lines of:

setTimeout(function() {
    console.log("First task")

    setTimeout(function() { 
        console.log("Second task");
    },1000);
},1000);

This would execute the first task, once called it will execute the second task

Edit: I saw another post about doing it non-async, you want to avoid doing anything non-async in JavaScript as it will hold up the browser which is general is a bad practice and bad user experience

Upvotes: 1

Trobol
Trobol

Reputation: 1250

From the MDN page:

The setTimeout() method ... sets a timer which executes a function or specified piece of code once the timer expires.

Upvotes: 0

Asim Khan
Asim Khan

Reputation: 2049

because setTimeout works asynchronously, means all of these 5 statements will be executed simultaneously and all of these will start waiting for 1 second. and after one second all will be executed. hope it clears.

Upvotes: 3

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