JavaScript scoping rules: how to use clearInterval() inside a callback

-1

I am trying to learn JS using a course on PluralSight, and I found this example which prints "hello world" every second, and stops after 5 seconds. This is the intended solution, and it works.

let counter = 0;

const intervalId = setInterval(() => {

  console.log('Hello World');

  counter += 1;



  if (counter === 5) {

    console.log('Done');

    clearInterval(intervalId);

  }

}, 1000);

I am trying to get it to use a callback instead of an inline function, but I am not able to capture intervalID. I tried passing 'this' as function argument, but that also doesn't work. What is the correct way here?

// doesn't work

let counter = 0;

const f = (intervalID) => {

    console.log("Hello World");

    counter += 1

    console.log(intervalID)

    if (counter ==5){

        console.log("Done")

        clearInterval(intervalID)

    }



}



const intervalID = setInterval(f, 1000)

asked Jan 3 at 1:16

Harshdeep Gupta

186

Remove the intervalID parameter. The first parameter to setInterval is A function to be executed every delay milliseconds. The function is not passed any parameters, and no return value is expected.

– CertainPerformance
Jan 3 at 1:18

add a comment |

-1

I am trying to learn JS using a course on PluralSight, and I found this example which prints "hello world" every second, and stops after 5 seconds. This is the intended solution, and it works.

let counter = 0;

const intervalId = setInterval(() => {

  console.log('Hello World');

  counter += 1;



  if (counter === 5) {

    console.log('Done');

    clearInterval(intervalId);

  }

}, 1000);

// doesn't work

let counter = 0;

const f = (intervalID) => {

    console.log("Hello World");

    counter += 1

    console.log(intervalID)

    if (counter ==5){

        console.log("Done")

        clearInterval(intervalID)

    }



}



const intervalID = setInterval(f, 1000)

asked Jan 3 at 1:16

Harshdeep Gupta

186

Remove the intervalID parameter. The first parameter to setInterval is A function to be executed every delay milliseconds. The function is not passed any parameters, and no return value is expected.

– CertainPerformance
Jan 3 at 1:18

add a comment |

-1

I am trying to learn JS using a course on PluralSight, and I found this example which prints "hello world" every second, and stops after 5 seconds. This is the intended solution, and it works.

let counter = 0;

const intervalId = setInterval(() => {

  console.log('Hello World');

  counter += 1;



  if (counter === 5) {

    console.log('Done');

    clearInterval(intervalId);

  }

}, 1000);

// doesn't work

let counter = 0;

const f = (intervalID) => {

    console.log("Hello World");

    counter += 1

    console.log(intervalID)

    if (counter ==5){

        console.log("Done")

        clearInterval(intervalID)

    }



}



const intervalID = setInterval(f, 1000)

asked Jan 3 at 1:16

Harshdeep Gupta

186

I am trying to learn JS using a course on PluralSight, and I found this example which prints "hello world" every second, and stops after 5 seconds. This is the intended solution, and it works.

let counter = 0;

const intervalId = setInterval(() => {

  console.log('Hello World');

  counter += 1;



  if (counter === 5) {

    console.log('Done');

    clearInterval(intervalId);

  }

}, 1000);

// doesn't work

let counter = 0;

const f = (intervalID) => {

    console.log("Hello World");

    counter += 1

    console.log(intervalID)

    if (counter ==5){

        console.log("Done")

        clearInterval(intervalID)

    }



}



const intervalID = setInterval(f, 1000)

javascript

asked Jan 3 at 1:16

Harshdeep Gupta

186

asked Jan 3 at 1:16

Harshdeep Gupta

186

asked Jan 3 at 1:16

Harshdeep Gupta

186

asked Jan 3 at 1:16

Harshdeep Gupta

186

asked Jan 3 at 1:16

Harshdeep Gupta

186

Remove the intervalID parameter. The first parameter to setInterval is A function to be executed every delay milliseconds. The function is not passed any parameters, and no return value is expected.

– CertainPerformance
Jan 3 at 1:18

add a comment |

Remove the intervalID parameter. The first parameter to setInterval is A function to be executed every delay milliseconds. The function is not passed any parameters, and no return value is expected.

– CertainPerformance
Jan 3 at 1:18

Remove the intervalID parameter. The first parameter to setInterval is

A function to be executed every delay milliseconds. The function is not passed any parameters, and no return value is expected.

– CertainPerformance
Jan 3 at 1:18

Remove the intervalID parameter. The first parameter to setInterval is

A function to be executed every delay milliseconds. The function is not passed any parameters, and no return value is expected.

– CertainPerformance
Jan 3 at 1:18

add a comment |

1 Answer
1

active

oldest

votes

Your intervalID is not an argument passed to f, but if you just remove the argument it will work because the intervalID is lexically scoped so that it's available inside f.

let counter = 0;

const f = () => {

    console.log("Hello World");

    counter += 1

    console.log(intervalID)

    if (counter ==5){

        console.log("Done")

        clearInterval(intervalID)

    }



}



const intervalID = setInterval(f, 1000)

OR passing in the intervalID is also fine:

let counter = 0;

const f = (intervalID) => {

    console.log("Hello World");

    counter += 1

    console.log(intervalID)

    if (counter ==5){

        console.log("Done")

        clearInterval(intervalID)

    }



}



const intervalID = setInterval(() => f(intervalID), 1000)

answered Jan 3 at 1:18

Adam

28.7k94464

Thanks a lot, the lexical scoping in JavaScript is really different. I don't even understand how is that possible! Can you explain a little bit more about it?

– Harshdeep Gupta
Jan 3 at 1:40

add a comment |

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1 Answer
1

active

oldest

votes

1 Answer
1

active

oldest

votes

Your intervalID is not an argument passed to f, but if you just remove the argument it will work because the intervalID is lexically scoped so that it's available inside f.

let counter = 0;

const f = () => {

    console.log("Hello World");

    counter += 1

    console.log(intervalID)

    if (counter ==5){

        console.log("Done")

        clearInterval(intervalID)

    }



}



const intervalID = setInterval(f, 1000)

OR passing in the intervalID is also fine:

let counter = 0;

const f = (intervalID) => {

    console.log("Hello World");

    counter += 1

    console.log(intervalID)

    if (counter ==5){

        console.log("Done")

        clearInterval(intervalID)

    }



}



const intervalID = setInterval(() => f(intervalID), 1000)

answered Jan 3 at 1:18

Adam

28.7k94464

Thanks a lot, the lexical scoping in JavaScript is really different. I don't even understand how is that possible! Can you explain a little bit more about it?

– Harshdeep Gupta
Jan 3 at 1:40

add a comment |

Your intervalID is not an argument passed to f, but if you just remove the argument it will work because the intervalID is lexically scoped so that it's available inside f.

let counter = 0;

const f = () => {

    console.log("Hello World");

    counter += 1

    console.log(intervalID)

    if (counter ==5){

        console.log("Done")

        clearInterval(intervalID)

    }



}



const intervalID = setInterval(f, 1000)

OR passing in the intervalID is also fine:

let counter = 0;

const f = (intervalID) => {

    console.log("Hello World");

    counter += 1

    console.log(intervalID)

    if (counter ==5){

        console.log("Done")

        clearInterval(intervalID)

    }



}



const intervalID = setInterval(() => f(intervalID), 1000)

answered Jan 3 at 1:18

Adam

28.7k94464

Thanks a lot, the lexical scoping in JavaScript is really different. I don't even understand how is that possible! Can you explain a little bit more about it?

– Harshdeep Gupta
Jan 3 at 1:40

add a comment |

Your intervalID is not an argument passed to f, but if you just remove the argument it will work because the intervalID is lexically scoped so that it's available inside f.

let counter = 0;

const f = () => {

    console.log("Hello World");

    counter += 1

    console.log(intervalID)

    if (counter ==5){

        console.log("Done")

        clearInterval(intervalID)

    }



}



const intervalID = setInterval(f, 1000)

OR passing in the intervalID is also fine:

let counter = 0;

const f = (intervalID) => {

    console.log("Hello World");

    counter += 1

    console.log(intervalID)

    if (counter ==5){

        console.log("Done")

        clearInterval(intervalID)

    }



}



const intervalID = setInterval(() => f(intervalID), 1000)

answered Jan 3 at 1:18

Adam

28.7k94464

Your intervalID is not an argument passed to f, but if you just remove the argument it will work because the intervalID is lexically scoped so that it's available inside f.

let counter = 0;

const f = () => {

    console.log("Hello World");

    counter += 1

    console.log(intervalID)

    if (counter ==5){

        console.log("Done")

        clearInterval(intervalID)

    }



}



const intervalID = setInterval(f, 1000)

OR passing in the intervalID is also fine:

let counter = 0;

const f = (intervalID) => {

    console.log("Hello World");

    counter += 1

    console.log(intervalID)

    if (counter ==5){

        console.log("Done")

        clearInterval(intervalID)

    }



}



const intervalID = setInterval(() => f(intervalID), 1000)

answered Jan 3 at 1:18

Adam

28.7k94464

answered Jan 3 at 1:18

Adam

28.7k94464

answered Jan 3 at 1:18

Adam

28.7k94464

answered Jan 3 at 1:18

Adam

28.7k94464

Thanks a lot, the lexical scoping in JavaScript is really different. I don't even understand how is that possible! Can you explain a little bit more about it?

– Harshdeep Gupta
Jan 3 at 1:40

add a comment |

Thanks a lot, the lexical scoping in JavaScript is really different. I don't even understand how is that possible! Can you explain a little bit more about it?

– Harshdeep Gupta
Jan 3 at 1:40

Thanks a lot, the lexical scoping in JavaScript is really different. I don't even understand how is that possible! Can you explain a little bit more about it?

– Harshdeep Gupta
Jan 3 at 1:40

add a comment |

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