Why does the event fire more than once?

up vote
-2
down vote

favorite

For the true boolean on eventListeners I read here:

once: A Boolean indicating that the listener should be invoked at most once after being added. If true, the listener would be automatically removed when invoked.

window.addEventListener("keydown", function(event){

    switch(event.code){

        case 'Digit1': 

            shoot('Ball1');

            break;



        case 'Digit2':

            shoot('Ball2');

            break;

    }

}, true);

In my code the function shoot is called endless. Why?

And how can I fix it? The function shoot() may start only once.

As recommended I changed 'true' into '{once: true}'. It still call shoot() endless. Do you have an idea, why?

Thanks to @CertainPerformance.

If you should have the same problem be aware, that the internet explorer doesn't know event.code.

edited Nov 22 at 9:21

asked Nov 22 at 7:26

NewbieXXL

397

Maybe you add the event listener more than once?
– yossico
Nov 22 at 7:30

Up to now this is the only event listener in my code. If another one will be neccessary, I can't say at this moment.
– NewbieXXL
Nov 22 at 7:33

add a comment |

up vote
-2
down vote

favorite

For the true boolean on eventListeners I read here:

once: A Boolean indicating that the listener should be invoked at most once after being added. If true, the listener would be automatically removed when invoked.

window.addEventListener("keydown", function(event){

    switch(event.code){

        case 'Digit1': 

            shoot('Ball1');

            break;



        case 'Digit2':

            shoot('Ball2');

            break;

    }

}, true);

In my code the function shoot is called endless. Why?

And how can I fix it? The function shoot() may start only once.

As recommended I changed 'true' into '{once: true}'. It still call shoot() endless. Do you have an idea, why?

Thanks to @CertainPerformance.

If you should have the same problem be aware, that the internet explorer doesn't know event.code.

edited Nov 22 at 9:21

asked Nov 22 at 7:26

NewbieXXL

397

Maybe you add the event listener more than once?
– yossico
Nov 22 at 7:30

Up to now this is the only event listener in my code. If another one will be neccessary, I can't say at this moment.
– NewbieXXL
Nov 22 at 7:33

add a comment |

up vote
-2
down vote

favorite

For the true boolean on eventListeners I read here:

once: A Boolean indicating that the listener should be invoked at most once after being added. If true, the listener would be automatically removed when invoked.

window.addEventListener("keydown", function(event){

    switch(event.code){

        case 'Digit1': 

            shoot('Ball1');

            break;



        case 'Digit2':

            shoot('Ball2');

            break;

    }

}, true);

In my code the function shoot is called endless. Why?

And how can I fix it? The function shoot() may start only once.

As recommended I changed 'true' into '{once: true}'. It still call shoot() endless. Do you have an idea, why?

Thanks to @CertainPerformance.

If you should have the same problem be aware, that the internet explorer doesn't know event.code.

edited Nov 22 at 9:21

asked Nov 22 at 7:26

NewbieXXL

397

For the true boolean on eventListeners I read here:

once: A Boolean indicating that the listener should be invoked at most once after being added. If true, the listener would be automatically removed when invoked.

window.addEventListener("keydown", function(event){

    switch(event.code){

        case 'Digit1': 

            shoot('Ball1');

            break;



        case 'Digit2':

            shoot('Ball2');

            break;

    }

}, true);

In my code the function shoot is called endless. Why?

And how can I fix it? The function shoot() may start only once.

As recommended I changed 'true' into '{once: true}'. It still call shoot() endless. Do you have an idea, why?

Thanks to @CertainPerformance.

If you should have the same problem be aware, that the internet explorer doesn't know event.code.

javascript addeventlistener

edited Nov 22 at 9:21

asked Nov 22 at 7:26

NewbieXXL

397

edited Nov 22 at 9:21

asked Nov 22 at 7:26

NewbieXXL

397

edited Nov 22 at 9:21

asked Nov 22 at 7:26

NewbieXXL

397

asked Nov 22 at 7:26

NewbieXXL

397

asked Nov 22 at 7:26

NewbieXXL

397

Maybe you add the event listener more than once?
– yossico
Nov 22 at 7:30

Up to now this is the only event listener in my code. If another one will be neccessary, I can't say at this moment.
– NewbieXXL
Nov 22 at 7:33

add a comment |

Maybe you add the event listener more than once?
– yossico
Nov 22 at 7:30

Up to now this is the only event listener in my code. If another one will be neccessary, I can't say at this moment.
– NewbieXXL
Nov 22 at 7:33

Maybe you add the event listener more than once?
– yossico
Nov 22 at 7:30

Up to now this is the only event listener in my code. If another one will be neccessary, I can't say at this moment.
– NewbieXXL
Nov 22 at 7:33

add a comment |

2 Answers
2

active

oldest

votes

up vote
3
down vote

The third parameter provided to addEventListener is either an options object, or useCapture, a boolean. Because you passed a boolean, the interpreter is considering you to have indicated that you want the function to trigger in the capturing phase, rather than the bubbling phase - which is not something you care about.

Pass an options object with a once property instead:

window.addEventListener(

  "keydown",

  function(event){

    switch(event.code){

      case 'Digit1': 

        shoot('Ball1');

        break;



      case 'Digit2':

        shoot('Ball2');

        break;

    }



  },

  { once: true }

);

window.addEventListener(

  "keydown",

  function(event){

    console.log('function running');

  },

  { once: true }

);

Internet Explorer and other older browser versions don't support the once option, so to support IE, you'll have to write a bit more code - manually remove the listener once it's triggered:

function listener() {

  console.log('function running');

  window.removeEventListener("keydown", listener);

}

window.addEventListener("keydown", listener);

Or, with the switch as well:

window.addEventListener("keydown", listener);



function listener(event) {

  console.log('function running');

  window.removeEventListener("keydown", listener);



  switch (event.code) {

    case 'Digit1':

      shoot('Ball1');

      break;



    case 'Digit2':

      shoot('Ball2');

      break;

  }

}

Again, with more switch cases:

window.addEventListener("keydown", listener); 



function listener(event) { 

  console.log('function running'); 

  window.removeEventListener("keydown", listener); 



  switch(event.code){ 

    case 'Digit1': 

      shoot('Ball1'); 

      break; 



    case 'Digit2': 

      shoot('Ball2'); 

      break; 



    case 'Digit3': 

      shoot('Ball3'); 

      break; 



    case 'Digit4': 

      shoot('Ball4'); 

      break; 

  }

}

edited Nov 22 at 8:34

answered Nov 22 at 7:33

CertainPerformance

73.1k143454

I have tryed it without success. It doesn't work in chrome or iexplorer :-(
– NewbieXXL
Nov 22 at 7:35

See snippet edited into answer, works perfectly fine for me
– CertainPerformance
Nov 22 at 7:37

I believe you. But why doesn't it work for me?
– NewbieXXL
Nov 22 at 7:38

For non-up-to-date browsers like IE, you can't use the once option, you'll have to do it manually with removeEventListener instead. Looks like browsers implemented it around the end of 2016
– CertainPerformance
Nov 22 at 7:41

I have replaced {once: true} with 'listener' function and added the function in my code. chrome still show the the endless behaviour and the iexplorer doesn't react on keydown.
– NewbieXXL
Nov 22 at 7:47

|
show 2 more comments

up vote
1
down vote

The boolean parameter you're adding doesn't specify that the event handler should only be executing once. It relates to event capture.

To have the handler execute only once, you need to pass an options object:

window.addEventListener("keydown", function(event) { /* ... */ }, {once: true});

answered Nov 22 at 7:33

Robby Cornelissen

42.9k126789

add a comment |

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2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

up vote
3
down vote

Pass an options object with a once property instead:

window.addEventListener(

  "keydown",

  function(event){

    switch(event.code){

      case 'Digit1': 

        shoot('Ball1');

        break;



      case 'Digit2':

        shoot('Ball2');

        break;

    }



  },

  { once: true }

);

window.addEventListener(

  "keydown",

  function(event){

    console.log('function running');

  },

  { once: true }

);

Internet Explorer and other older browser versions don't support the once option, so to support IE, you'll have to write a bit more code - manually remove the listener once it's triggered:

function listener() {

  console.log('function running');

  window.removeEventListener("keydown", listener);

}

window.addEventListener("keydown", listener);

Or, with the switch as well:

window.addEventListener("keydown", listener);



function listener(event) {

  console.log('function running');

  window.removeEventListener("keydown", listener);



  switch (event.code) {

    case 'Digit1':

      shoot('Ball1');

      break;



    case 'Digit2':

      shoot('Ball2');

      break;

  }

}

Again, with more switch cases:

window.addEventListener("keydown", listener); 



function listener(event) { 

  console.log('function running'); 

  window.removeEventListener("keydown", listener); 



  switch(event.code){ 

    case 'Digit1': 

      shoot('Ball1'); 

      break; 



    case 'Digit2': 

      shoot('Ball2'); 

      break; 



    case 'Digit3': 

      shoot('Ball3'); 

      break; 



    case 'Digit4': 

      shoot('Ball4'); 

      break; 

  }

}

edited Nov 22 at 8:34

answered Nov 22 at 7:33

CertainPerformance

73.1k143454

I have tryed it without success. It doesn't work in chrome or iexplorer :-(
– NewbieXXL
Nov 22 at 7:35

See snippet edited into answer, works perfectly fine for me
– CertainPerformance
Nov 22 at 7:37

I believe you. But why doesn't it work for me?
– NewbieXXL
Nov 22 at 7:38

For non-up-to-date browsers like IE, you can't use the once option, you'll have to do it manually with removeEventListener instead. Looks like browsers implemented it around the end of 2016
– CertainPerformance
Nov 22 at 7:41

I have replaced {once: true} with 'listener' function and added the function in my code. chrome still show the the endless behaviour and the iexplorer doesn't react on keydown.
– NewbieXXL
Nov 22 at 7:47

|
show 2 more comments

up vote
3
down vote

Pass an options object with a once property instead:

window.addEventListener(

  "keydown",

  function(event){

    switch(event.code){

      case 'Digit1': 

        shoot('Ball1');

        break;



      case 'Digit2':

        shoot('Ball2');

        break;

    }



  },

  { once: true }

);

window.addEventListener(

  "keydown",

  function(event){

    console.log('function running');

  },

  { once: true }

);

Internet Explorer and other older browser versions don't support the once option, so to support IE, you'll have to write a bit more code - manually remove the listener once it's triggered:

function listener() {

  console.log('function running');

  window.removeEventListener("keydown", listener);

}

window.addEventListener("keydown", listener);

Or, with the switch as well:

window.addEventListener("keydown", listener);



function listener(event) {

  console.log('function running');

  window.removeEventListener("keydown", listener);



  switch (event.code) {

    case 'Digit1':

      shoot('Ball1');

      break;



    case 'Digit2':

      shoot('Ball2');

      break;

  }

}

Again, with more switch cases:

window.addEventListener("keydown", listener); 



function listener(event) { 

  console.log('function running'); 

  window.removeEventListener("keydown", listener); 



  switch(event.code){ 

    case 'Digit1': 

      shoot('Ball1'); 

      break; 



    case 'Digit2': 

      shoot('Ball2'); 

      break; 



    case 'Digit3': 

      shoot('Ball3'); 

      break; 



    case 'Digit4': 

      shoot('Ball4'); 

      break; 

  }

}

edited Nov 22 at 8:34

answered Nov 22 at 7:33

CertainPerformance

73.1k143454

I have tryed it without success. It doesn't work in chrome or iexplorer :-(
– NewbieXXL
Nov 22 at 7:35

See snippet edited into answer, works perfectly fine for me
– CertainPerformance
Nov 22 at 7:37

I believe you. But why doesn't it work for me?
– NewbieXXL
Nov 22 at 7:38

For non-up-to-date browsers like IE, you can't use the once option, you'll have to do it manually with removeEventListener instead. Looks like browsers implemented it around the end of 2016
– CertainPerformance
Nov 22 at 7:41

I have replaced {once: true} with 'listener' function and added the function in my code. chrome still show the the endless behaviour and the iexplorer doesn't react on keydown.
– NewbieXXL
Nov 22 at 7:47

|
show 2 more comments

up vote
3
down vote

Pass an options object with a once property instead:

window.addEventListener(

  "keydown",

  function(event){

    switch(event.code){

      case 'Digit1': 

        shoot('Ball1');

        break;



      case 'Digit2':

        shoot('Ball2');

        break;

    }



  },

  { once: true }

);

window.addEventListener(

  "keydown",

  function(event){

    console.log('function running');

  },

  { once: true }

);

Internet Explorer and other older browser versions don't support the once option, so to support IE, you'll have to write a bit more code - manually remove the listener once it's triggered:

function listener() {

  console.log('function running');

  window.removeEventListener("keydown", listener);

}

window.addEventListener("keydown", listener);

Or, with the switch as well:

window.addEventListener("keydown", listener);



function listener(event) {

  console.log('function running');

  window.removeEventListener("keydown", listener);



  switch (event.code) {

    case 'Digit1':

      shoot('Ball1');

      break;



    case 'Digit2':

      shoot('Ball2');

      break;

  }

}

Again, with more switch cases:

window.addEventListener("keydown", listener); 



function listener(event) { 

  console.log('function running'); 

  window.removeEventListener("keydown", listener); 



  switch(event.code){ 

    case 'Digit1': 

      shoot('Ball1'); 

      break; 



    case 'Digit2': 

      shoot('Ball2'); 

      break; 



    case 'Digit3': 

      shoot('Ball3'); 

      break; 



    case 'Digit4': 

      shoot('Ball4'); 

      break; 

  }

}

edited Nov 22 at 8:34

answered Nov 22 at 7:33

CertainPerformance

73.1k143454

Pass an options object with a once property instead:

window.addEventListener(

  "keydown",

  function(event){

    switch(event.code){

      case 'Digit1': 

        shoot('Ball1');

        break;



      case 'Digit2':

        shoot('Ball2');

        break;

    }



  },

  { once: true }

);

window.addEventListener(

  "keydown",

  function(event){

    console.log('function running');

  },

  { once: true }

);

Internet Explorer and other older browser versions don't support the once option, so to support IE, you'll have to write a bit more code - manually remove the listener once it's triggered:

function listener() {

  console.log('function running');

  window.removeEventListener("keydown", listener);

}

window.addEventListener("keydown", listener);

Or, with the switch as well:

window.addEventListener("keydown", listener);



function listener(event) {

  console.log('function running');

  window.removeEventListener("keydown", listener);



  switch (event.code) {

    case 'Digit1':

      shoot('Ball1');

      break;



    case 'Digit2':

      shoot('Ball2');

      break;

  }

}

Again, with more switch cases:

window.addEventListener("keydown", listener); 



function listener(event) { 

  console.log('function running'); 

  window.removeEventListener("keydown", listener); 



  switch(event.code){ 

    case 'Digit1': 

      shoot('Ball1'); 

      break; 



    case 'Digit2': 

      shoot('Ball2'); 

      break; 



    case 'Digit3': 

      shoot('Ball3'); 

      break; 



    case 'Digit4': 

      shoot('Ball4'); 

      break; 

  }

}

window.addEventListener(

  "keydown",

  function(event){

    console.log('function running');

  },

  { once: true }

);

window.addEventListener(

  "keydown",

  function(event){

    console.log('function running');

  },

  { once: true }

);

function listener() {

  console.log('function running');

  window.removeEventListener("keydown", listener);

}

window.addEventListener("keydown", listener);

function listener() {

  console.log('function running');

  window.removeEventListener("keydown", listener);

}

window.addEventListener("keydown", listener);

window.addEventListener("keydown", listener);



function listener(event) {

  console.log('function running');

  window.removeEventListener("keydown", listener);



  switch (event.code) {

    case 'Digit1':

      shoot('Ball1');

      break;



    case 'Digit2':

      shoot('Ball2');

      break;

  }

}

window.addEventListener("keydown", listener);



function listener(event) {

  console.log('function running');

  window.removeEventListener("keydown", listener);



  switch (event.code) {

    case 'Digit1':

      shoot('Ball1');

      break;



    case 'Digit2':

      shoot('Ball2');

      break;

  }

}

window.addEventListener("keydown", listener); 



function listener(event) { 

  console.log('function running'); 

  window.removeEventListener("keydown", listener); 



  switch(event.code){ 

    case 'Digit1': 

      shoot('Ball1'); 

      break; 



    case 'Digit2': 

      shoot('Ball2'); 

      break; 



    case 'Digit3': 

      shoot('Ball3'); 

      break; 



    case 'Digit4': 

      shoot('Ball4'); 

      break; 

  }

}

window.addEventListener("keydown", listener); 



function listener(event) { 

  console.log('function running'); 

  window.removeEventListener("keydown", listener); 



  switch(event.code){ 

    case 'Digit1': 

      shoot('Ball1'); 

      break; 



    case 'Digit2': 

      shoot('Ball2'); 

      break; 



    case 'Digit3': 

      shoot('Ball3'); 

      break; 



    case 'Digit4': 

      shoot('Ball4'); 

      break; 

  }

}

edited Nov 22 at 8:34

answered Nov 22 at 7:33

CertainPerformance

73.1k143454

edited Nov 22 at 8:34

answered Nov 22 at 7:33

CertainPerformance

73.1k143454

answered Nov 22 at 7:33

CertainPerformance

73.1k143454

answered Nov 22 at 7:33

CertainPerformance

73.1k143454

I have tryed it without success. It doesn't work in chrome or iexplorer :-(
– NewbieXXL
Nov 22 at 7:35

See snippet edited into answer, works perfectly fine for me
– CertainPerformance
Nov 22 at 7:37

I believe you. But why doesn't it work for me?
– NewbieXXL
Nov 22 at 7:38

For non-up-to-date browsers like IE, you can't use the once option, you'll have to do it manually with removeEventListener instead. Looks like browsers implemented it around the end of 2016
– CertainPerformance
Nov 22 at 7:41

I have replaced {once: true} with 'listener' function and added the function in my code. chrome still show the the endless behaviour and the iexplorer doesn't react on keydown.
– NewbieXXL
Nov 22 at 7:47

|
show 2 more comments

I have tryed it without success. It doesn't work in chrome or iexplorer :-(
– NewbieXXL
Nov 22 at 7:35

See snippet edited into answer, works perfectly fine for me
– CertainPerformance
Nov 22 at 7:37

I believe you. But why doesn't it work for me?
– NewbieXXL
Nov 22 at 7:38

For non-up-to-date browsers like IE, you can't use the once option, you'll have to do it manually with removeEventListener instead. Looks like browsers implemented it around the end of 2016
– CertainPerformance
Nov 22 at 7:41

I have replaced {once: true} with 'listener' function and added the function in my code. chrome still show the the endless behaviour and the iexplorer doesn't react on keydown.
– NewbieXXL
Nov 22 at 7:47

I have tryed it without success. It doesn't work in chrome or iexplorer :-(
– NewbieXXL
Nov 22 at 7:35

See snippet edited into answer, works perfectly fine for me
– CertainPerformance
Nov 22 at 7:37

I believe you. But why doesn't it work for me?
– NewbieXXL
Nov 22 at 7:38

For non-up-to-date browsers like IE, you can't use the once option, you'll have to do it manually with removeEventListener instead. Looks like browsers implemented it around the end of 2016
– CertainPerformance
Nov 22 at 7:41

I have replaced {once: true} with 'listener' function and added the function in my code. chrome still show the the endless behaviour and the iexplorer doesn't react on keydown.
– NewbieXXL
Nov 22 at 7:47

|
show 2 more comments

up vote
1
down vote

The boolean parameter you're adding doesn't specify that the event handler should only be executing once. It relates to event capture.

To have the handler execute only once, you need to pass an options object:

window.addEventListener("keydown", function(event) { /* ... */ }, {once: true});

answered Nov 22 at 7:33

Robby Cornelissen

42.9k126789

add a comment |

up vote
1
down vote

The boolean parameter you're adding doesn't specify that the event handler should only be executing once. It relates to event capture.

To have the handler execute only once, you need to pass an options object:

window.addEventListener("keydown", function(event) { /* ... */ }, {once: true});

answered Nov 22 at 7:33

Robby Cornelissen

42.9k126789

add a comment |

up vote
1
down vote

The boolean parameter you're adding doesn't specify that the event handler should only be executing once. It relates to event capture.

To have the handler execute only once, you need to pass an options object:

window.addEventListener("keydown", function(event) { /* ... */ }, {once: true});

answered Nov 22 at 7:33

Robby Cornelissen

42.9k126789

The boolean parameter you're adding doesn't specify that the event handler should only be executing once. It relates to event capture.

To have the handler execute only once, you need to pass an options object:

window.addEventListener("keydown", function(event) { /* ... */ }, {once: true});

answered Nov 22 at 7:33

Robby Cornelissen

42.9k126789

answered Nov 22 at 7:33

Robby Cornelissen

42.9k126789

answered Nov 22 at 7:33

Robby Cornelissen

42.9k126789

answered Nov 22 at 7:33

Robby Cornelissen

42.9k126789

add a comment |

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