Function for an event

Function for an event - javascript

I would like to create a function from this:
element.onclick = function(e){
... code ...
}
To something like this:
element.onclick = doSomething(e);
element2.onclick = doSomething(e);
function doSomething(e){
... code ...
}
In this way I could call the function multiple times but in this way e is not passed as an event so doesn't works.
How should I do this?

Not sure exactly what you mean, but you can declare a function and use it as the handler for multiple elements. The event argument will still be passed.
element.onclick = someHandler;
anotherElem.onclick = someHandler;
yetAnotherElem.onclick = someHandler;
function someHandler(e){
e = e || event;
... code ...
}
Each of the 3 elements will call the same handler, and have the event object as its argument.
EDIT: With regard to your edit, you were calling the function and assigning its return value to onclick instead of assigning the function itself.
Seems from your comment that you figured that out though. :o)

function onClickHandler(e){
//Do stuff...
}
element.onclick = onClickHandler;

I think you are asking how to create a normal function and use it in various ways?
function fnName(e) {
... code ...
}
Can be used in various ways:
element.onclick = fnName;
fnName();
//Call it however you like?

First you gotta give your function a name.
function clickEvent(e) {
... do stuff ...
}
Then attach it onto the element like this:
element.onClick = clickEvent;
When the event is triggered, the event will automatically get passed into the function.

You need to write it in the form of:
function fnName(e){
... code ...
}
and then you can call fnName and pass the variable you need.
If your function does not really need the 'e', you can write
function fnName(){
...code...
}

you can do this:
element.onclick = function(e){
myfunc();
}
function myfunc()
{
... code
}

Related

Probably a really simple thing but I can't seem to pass an argument into my Javascript function [duplicate]

The situation is somewhat like-
var someVar = some_other_function();
someObj.addEventListener("click", function(){
some_function(someVar);
}, false);
The problem is that the value of someVar is not visible inside the listener function of the addEventListener, where it is probably being treated as a new variable.

Why not just get the arguments from the target attribute of the event?
Example:
const someInput = document.querySelector('button');
someInput.addEventListener('click', myFunc, false);
someInput.myParam = 'This is my parameter';
function myFunc(evt)
{
window.alert(evt.currentTarget.myParam);
}
<button class="input">Show parameter</button>
JavaScript is a prototype-oriented language, remember!

There is absolutely nothing wrong with the code you've written. Both some_function and someVar should be accessible, in case they were available in the context where anonymous
function() { some_function(someVar); }
was created.
Check if the alert gives you the value you've been looking for, be sure it will be accessible in the scope of anonymous function (unless you have more code that operates on the same someVar variable next to the call to addEventListener)
var someVar;
someVar = some_other_function();
alert(someVar);
someObj.addEventListener("click", function(){
some_function(someVar);
}, false);

This question is old but I thought I'd offer an alternative using ES5's .bind() - for posterity. :)
function some_func(otherFunc, ev) {
// magic happens
}
someObj.addEventListener("click", some_func.bind(null, some_other_func), false);
Just be aware that you need to set up your listener function with the first param as the argument you're passing into bind (your other function) and the second param is now the event (instead of the first, as it would have been).

Quite and old question but I had the same issue today. Cleanest solution I found is to use the concept of currying.
The code for that:
someObj.addEventListener('click', some_function(someVar));
var some_function = function(someVar) {
return function curried_func(e) {
// do something here
}
}
By naming the curried function it allows you to call Object.removeEventListener to unregister the eventListener at a later execution time.

You can just bind all necessary arguments with 'bind':
root.addEventListener('click', myPrettyHandler.bind(null, event, arg1, ... ));
In this way you'll always get the event, arg1, and other stuff passed to myPrettyHandler.
http://passy.svbtle.com/partial-application-in-javascript-using-bind

nice one line alternative
element.addEventListener('dragstart',(evt) => onDragStart(param1, param2, param3, evt));
function onDragStart(param1, param2, param3, evt) {
//some action...
}

You can add and remove eventlisteners with arguments by declaring a function as a variable.
myaudio.addEventListener('ended',funcName=function(){newSrc(myaudio)},false);
newSrc is the method with myaudio as parameter
funcName is the function name variable
You can remove the listener with
myaudio.removeEventListener('ended',func,false);

Function.prototype.bind() is the way to bind a target function to a particular scope and optionally define the this object within the target function.
someObj.addEventListener("click", some_function.bind(this), false);
Or to capture some of the lexical scope, for example in a loop:
someObj.addEventListener("click", some_function.bind(this, arg1, arg2), false);
Finally, if the this parameter is not needed within the target function:
someObj.addEventListener("click", some_function.bind(null, arg1, arg2), false);

You could pass somevar by value(not by reference) via a javascript feature known as closure:
var someVar='origin';
func = function(v){
console.log(v);
}
document.addEventListener('click',function(someVar){
return function(){func(someVar)}
}(someVar));
someVar='changed'
Or you could write a common wrap function such as wrapEventCallback:
function wrapEventCallback(callback){
var args = Array.prototype.slice.call(arguments, 1);
return function(e){
callback.apply(this, args)
}
}
var someVar='origin';
func = function(v){
console.log(v);
}
document.addEventListener('click',wrapEventCallback(func,someVar))
someVar='changed'
Here wrapEventCallback(func,var1,var2) is like:
func.bind(null, var1,var2)

Here's yet another way (This one works inside for loops):
var someVar = some_other_function();
someObj.addEventListener("click",
function(theVar){
return function(){some_function(theVar)};
}(someVar),
false);

someVar value should be accessible only in some_function() context, not from listener's.
If you like to have it within listener, you must do something like:
someObj.addEventListener("click",
function(){
var newVar = someVar;
some_function(someVar);
},
false);
and use newVar instead.
The other way is to return someVar value from some_function() for using it further in listener (as a new local var):
var someVar = some_function(someVar);

one easy way to execute that may be this
window.addEventListener('click', (e) => functionHandler(e, ...args));
Works for me.

Use
el.addEventListener('click',
function(){
// this will give you the id value
alert(this.id);
},
false);
And if you want to pass any custom value into this anonymous function then the easiest way to do it is
// this will dynamically create property a property
// you can create anything like el.<your variable>
el.myvalue = "hello world";
el.addEventListener('click',
function(){
//this will show you the myvalue
alert(el.myvalue);
// this will give you the id value
alert(this.id);
},
false);
Works perfectly in my project. Hope this will help

If I'm not mistaken using calling the function with bind actually creates a new function that is returned by the bind method. This will cause you problems later or if you would like to remove the event listener, as it's basically like an anonymous function:
// Possible:
function myCallback() { /* code here */ }
someObject.addEventListener('event', myCallback);
someObject.removeEventListener('event', myCallback);
// Not Possible:
function myCallback() { /* code here */ }
someObject.addEventListener('event', function() { myCallback });
someObject.removeEventListener('event', /* can't remove anonymous function */);
So take that in mind.
If you are using ES6 you could do the same as suggested but a bit cleaner:
someObject.addEventListener('event', () => myCallback(params));

$form.addEventListener('submit', save.bind(null, data, keyword, $name.value, myStemComment));
function save(data, keyword, name, comment, event) {
This is how I got event passed properly.

One way is doing this with an outer function:
elem.addEventListener('click', (function(numCopy) {
return function() {
alert(numCopy)
};
})(num));
This method of wrapping an anonymous function in parentheses and calling it right away is called an IIFE (Immediately-Invoked Function Expression)
You can check an example with two parameters in http://codepen.io/froucher/pen/BoWwgz.
catimg.addEventListener('click', (function(c, i){
return function() {
c.meows++;
i.textContent = c.name + '\'s meows are: ' + c.meows;
}
})(cat, catmeows));

In 2019, lots of api changes, the best answer no longer works, without fix bug.
share some working code.
Inspired by all above answer.
button_element = document.getElementById('your-button')
button_element.setAttribute('your-parameter-name',your-parameter-value);
button_element.addEventListener('click', your_function);
function your_function(event)
{
//when click print the parameter value
console.log(event.currentTarget.attributes.your-parameter-name.value;)
}

Sending arguments to an eventListener's callback function requires creating an isolated function and passing arguments to that isolated function.
Here's a nice little helper function you can use. Based on "hello world's" example above.)
One thing that is also needed is to maintain a reference to the function so we can remove the listener cleanly.
// Lambda closure chaos.
//
// Send an anonymous function to the listener, but execute it immediately.
// This will cause the arguments are captured, which is useful when running
// within loops.
//
// The anonymous function returns a closure, that will be executed when
// the event triggers. And since the arguments were captured, any vars
// that were sent in will be unique to the function.
function addListenerWithArgs(elem, evt, func, vars){
var f = function(ff, vv){
return (function (){
ff(vv);
});
}(func, vars);
elem.addEventListener(evt, f);
return f;
}
// Usage:
function doSomething(withThis){
console.log("withThis", withThis);
}
// Capture the function so we can remove it later.
var storeFunc = addListenerWithArgs(someElem, "click", doSomething, "foo");
// To remove the listener, use the normal routine:
someElem.removeEventListener("click", storeFunc);

There is a special variable inside all functions: arguments. You can pass your parameters as anonymous parameters and access them (by order) through the arguments variable.
Example:
var someVar = some_other_function();
someObj.addEventListener("click", function(someVar){
some_function(arguments[0]);
}, false);

I was stuck in this as I was using it in a loop for finding elements and adding listner to it. If you're using it in a loop, then this will work perfectly
for (var i = 0; i < states_array.length; i++) {
var link = document.getElementById('apply_'+states_array[i].state_id);
link.my_id = i;
link.addEventListener('click', function(e) {
alert(e.target.my_id);
some_function(states_array[e.target.my_id].css_url);
});
}

I suggest you to do something like that:
var someVar = some_other_function();
someObj.addEventListener("click", (event, param1 = someVar) => {
some_function(param1);
}, false);

The PERFECT SOLUTION for this is to use Closures like this:
function makeSizer(size) {
return function () {
document.body.style.fontSize = `${size}px`;
};
}
//pass parameters here and keep the reference in variables:
const size12 = makeSizer(12);
const size24 = makeSizer(24);
const size36 = makeSizer(36);
document.getElementById('size-12').addEventListener("click", size12);
document.getElementById('size-24').addEventListener("click", size24);
document.getElementById('size-36').addEventListener("click", size36);
document.getElementById('remove-12').addEventListener("click", ()=>{
document.getElementById('size-12').removeEventListener("click", size12);
alert("Now click on 'size 12' button and you will see that there is no event listener any more");
});
test<br/>
<button id="size-12">
size 12
</button>
<button id="size-24">
size 24
</button>
<button id="size-36">
size 36
</button>
<button id="remove-12">
remove 12
</button>
So basically you wrap a function inside another function and assign that to a variable that you can register as an event listener, but also unregister as well!

Also try these (IE8 + Chrome. I dont know for FF):
function addEvent(obj, type, fn) {
eval('obj.on'+type+'=fn');
}
function removeEvent(obj, type) {
eval('obj.on'+type+'=null');
}
// Use :
function someFunction (someArg) {alert(someArg);}
var object=document.getElementById('somObject_id') ;
var someArg="Hi there !";
var func=function(){someFunction (someArg)};
// mouseover is inactive
addEvent (object, 'mouseover', func);
// mouseover is now active
addEvent (object, 'mouseover');
// mouseover is inactive
Hope there is no typos :-)

The following answer is correct but the below code is not working in IE8 if suppose you compressed the js file using yuicompressor. (In fact,still most of the US peoples using IE8)
var someVar;
someVar = some_other_function();
alert(someVar);
someObj.addEventListener("click",
function(){
some_function(someVar);
},
false);
So, we can fix the above issue as follows and it works fine in all browsers
var someVar, eventListnerFunc;
someVar = some_other_function();
eventListnerFunc = some_function(someVar);
someObj.addEventListener("click", eventListnerFunc, false);
Hope, it would be useful for some one who is compressing the js file in production environment.
Good Luck!!

var EV = {
ev: '',
fn: '',
elem: '',
add: function () {
this.elem.addEventListener(this.ev, this.fn, false);
}
};
function cons() {
console.log('some what');
}
EV.ev = 'click';
EV.fn = cons;
EV.elem = document.getElementById('body');
EV.add();
//If you want to add one more listener for load event then simply add this two lines of code:
EV.ev = 'load';
EV.add();

The following approach worked well for me. Modified from here.
function callback(theVar) {
return function() {
theVar();
}
}
function some_other_function() {
document.body.innerHTML += "made it.";
}
var someVar = some_other_function;
document.getElementById('button').addEventListener('click', callback(someVar));
<!DOCTYPE html>
<html>
<body>
<button type="button" id="button">Click Me!</button>
</body>
</html>

Since your event listener is 'click', you can:
someObj.setAttribute("onclick", "function(parameter)");

Another workaround is by Using data attributes
function func(){
console.log(this.dataset.someVar);
div.removeEventListener("click", func);
}
var div = document.getElementById("some-div");
div.setAttribute("data-some-var", "hello");
div.addEventListener("click", func);
jsfiddle

The following code worked fine for me (firefox):
for (var i=0; i<3; i++) {
element = new ... // create your element
element.counter = i;
element.addEventListener('click', function(e){
console.log(this.counter);
... // another code with this element
}, false);
}
Output:
0
1
2

You need:
newElem.addEventListener('click', {
handleEvent: function (event) {
clickImg(parameter);
}
});

Attaching different eventListeners for each item in for-of-loop [duplicate]

The situation is somewhat like-
var someVar = some_other_function();
someObj.addEventListener("click", function(){
some_function(someVar);
}, false);
The problem is that the value of someVar is not visible inside the listener function of the addEventListener, where it is probably being treated as a new variable.

Why not just get the arguments from the target attribute of the event?
Example:
const someInput = document.querySelector('button');
someInput.addEventListener('click', myFunc, false);
someInput.myParam = 'This is my parameter';
function myFunc(evt)
{
window.alert(evt.currentTarget.myParam);
}
<button class="input">Show parameter</button>
JavaScript is a prototype-oriented language, remember!

There is absolutely nothing wrong with the code you've written. Both some_function and someVar should be accessible, in case they were available in the context where anonymous
function() { some_function(someVar); }
was created.
Check if the alert gives you the value you've been looking for, be sure it will be accessible in the scope of anonymous function (unless you have more code that operates on the same someVar variable next to the call to addEventListener)
var someVar;
someVar = some_other_function();
alert(someVar);
someObj.addEventListener("click", function(){
some_function(someVar);
}, false);

This question is old but I thought I'd offer an alternative using ES5's .bind() - for posterity. :)
function some_func(otherFunc, ev) {
// magic happens
}
someObj.addEventListener("click", some_func.bind(null, some_other_func), false);
Just be aware that you need to set up your listener function with the first param as the argument you're passing into bind (your other function) and the second param is now the event (instead of the first, as it would have been).

Quite and old question but I had the same issue today. Cleanest solution I found is to use the concept of currying.
The code for that:
someObj.addEventListener('click', some_function(someVar));
var some_function = function(someVar) {
return function curried_func(e) {
// do something here
}
}
By naming the curried function it allows you to call Object.removeEventListener to unregister the eventListener at a later execution time.

You can just bind all necessary arguments with 'bind':
root.addEventListener('click', myPrettyHandler.bind(null, event, arg1, ... ));
In this way you'll always get the event, arg1, and other stuff passed to myPrettyHandler.
http://passy.svbtle.com/partial-application-in-javascript-using-bind

nice one line alternative
element.addEventListener('dragstart',(evt) => onDragStart(param1, param2, param3, evt));
function onDragStart(param1, param2, param3, evt) {
//some action...
}

You can add and remove eventlisteners with arguments by declaring a function as a variable.
myaudio.addEventListener('ended',funcName=function(){newSrc(myaudio)},false);
newSrc is the method with myaudio as parameter
funcName is the function name variable
You can remove the listener with
myaudio.removeEventListener('ended',func,false);

Function.prototype.bind() is the way to bind a target function to a particular scope and optionally define the this object within the target function.
someObj.addEventListener("click", some_function.bind(this), false);
Or to capture some of the lexical scope, for example in a loop:
someObj.addEventListener("click", some_function.bind(this, arg1, arg2), false);
Finally, if the this parameter is not needed within the target function:
someObj.addEventListener("click", some_function.bind(null, arg1, arg2), false);

You could pass somevar by value(not by reference) via a javascript feature known as closure:
var someVar='origin';
func = function(v){
console.log(v);
}
document.addEventListener('click',function(someVar){
return function(){func(someVar)}
}(someVar));
someVar='changed'
Or you could write a common wrap function such as wrapEventCallback:
function wrapEventCallback(callback){
var args = Array.prototype.slice.call(arguments, 1);
return function(e){
callback.apply(this, args)
}
}
var someVar='origin';
func = function(v){
console.log(v);
}
document.addEventListener('click',wrapEventCallback(func,someVar))
someVar='changed'
Here wrapEventCallback(func,var1,var2) is like:
func.bind(null, var1,var2)

Here's yet another way (This one works inside for loops):
var someVar = some_other_function();
someObj.addEventListener("click",
function(theVar){
return function(){some_function(theVar)};
}(someVar),
false);

someVar value should be accessible only in some_function() context, not from listener's.
If you like to have it within listener, you must do something like:
someObj.addEventListener("click",
function(){
var newVar = someVar;
some_function(someVar);
},
false);
and use newVar instead.
The other way is to return someVar value from some_function() for using it further in listener (as a new local var):
var someVar = some_function(someVar);

one easy way to execute that may be this
window.addEventListener('click', (e) => functionHandler(e, ...args));
Works for me.

Use
el.addEventListener('click',
function(){
// this will give you the id value
alert(this.id);
},
false);
And if you want to pass any custom value into this anonymous function then the easiest way to do it is
// this will dynamically create property a property
// you can create anything like el.<your variable>
el.myvalue = "hello world";
el.addEventListener('click',
function(){
//this will show you the myvalue
alert(el.myvalue);
// this will give you the id value
alert(this.id);
},
false);
Works perfectly in my project. Hope this will help

If I'm not mistaken using calling the function with bind actually creates a new function that is returned by the bind method. This will cause you problems later or if you would like to remove the event listener, as it's basically like an anonymous function:
// Possible:
function myCallback() { /* code here */ }
someObject.addEventListener('event', myCallback);
someObject.removeEventListener('event', myCallback);
// Not Possible:
function myCallback() { /* code here */ }
someObject.addEventListener('event', function() { myCallback });
someObject.removeEventListener('event', /* can't remove anonymous function */);
So take that in mind.
If you are using ES6 you could do the same as suggested but a bit cleaner:
someObject.addEventListener('event', () => myCallback(params));

$form.addEventListener('submit', save.bind(null, data, keyword, $name.value, myStemComment));
function save(data, keyword, name, comment, event) {
This is how I got event passed properly.

One way is doing this with an outer function:
elem.addEventListener('click', (function(numCopy) {
return function() {
alert(numCopy)
};
})(num));
This method of wrapping an anonymous function in parentheses and calling it right away is called an IIFE (Immediately-Invoked Function Expression)
You can check an example with two parameters in http://codepen.io/froucher/pen/BoWwgz.
catimg.addEventListener('click', (function(c, i){
return function() {
c.meows++;
i.textContent = c.name + '\'s meows are: ' + c.meows;
}
})(cat, catmeows));

In 2019, lots of api changes, the best answer no longer works, without fix bug.
share some working code.
Inspired by all above answer.
button_element = document.getElementById('your-button')
button_element.setAttribute('your-parameter-name',your-parameter-value);
button_element.addEventListener('click', your_function);
function your_function(event)
{
//when click print the parameter value
console.log(event.currentTarget.attributes.your-parameter-name.value;)
}

Sending arguments to an eventListener's callback function requires creating an isolated function and passing arguments to that isolated function.
Here's a nice little helper function you can use. Based on "hello world's" example above.)
One thing that is also needed is to maintain a reference to the function so we can remove the listener cleanly.
// Lambda closure chaos.
//
// Send an anonymous function to the listener, but execute it immediately.
// This will cause the arguments are captured, which is useful when running
// within loops.
//
// The anonymous function returns a closure, that will be executed when
// the event triggers. And since the arguments were captured, any vars
// that were sent in will be unique to the function.
function addListenerWithArgs(elem, evt, func, vars){
var f = function(ff, vv){
return (function (){
ff(vv);
});
}(func, vars);
elem.addEventListener(evt, f);
return f;
}
// Usage:
function doSomething(withThis){
console.log("withThis", withThis);
}
// Capture the function so we can remove it later.
var storeFunc = addListenerWithArgs(someElem, "click", doSomething, "foo");
// To remove the listener, use the normal routine:
someElem.removeEventListener("click", storeFunc);

There is a special variable inside all functions: arguments. You can pass your parameters as anonymous parameters and access them (by order) through the arguments variable.
Example:
var someVar = some_other_function();
someObj.addEventListener("click", function(someVar){
some_function(arguments[0]);
}, false);

I was stuck in this as I was using it in a loop for finding elements and adding listner to it. If you're using it in a loop, then this will work perfectly
for (var i = 0; i < states_array.length; i++) {
var link = document.getElementById('apply_'+states_array[i].state_id);
link.my_id = i;
link.addEventListener('click', function(e) {
alert(e.target.my_id);
some_function(states_array[e.target.my_id].css_url);
});
}

I suggest you to do something like that:
var someVar = some_other_function();
someObj.addEventListener("click", (event, param1 = someVar) => {
some_function(param1);
}, false);

The PERFECT SOLUTION for this is to use Closures like this:
function makeSizer(size) {
return function () {
document.body.style.fontSize = `${size}px`;
};
}
//pass parameters here and keep the reference in variables:
const size12 = makeSizer(12);
const size24 = makeSizer(24);
const size36 = makeSizer(36);
document.getElementById('size-12').addEventListener("click", size12);
document.getElementById('size-24').addEventListener("click", size24);
document.getElementById('size-36').addEventListener("click", size36);
document.getElementById('remove-12').addEventListener("click", ()=>{
document.getElementById('size-12').removeEventListener("click", size12);
alert("Now click on 'size 12' button and you will see that there is no event listener any more");
});
test<br/>
<button id="size-12">
size 12
</button>
<button id="size-24">
size 24
</button>
<button id="size-36">
size 36
</button>
<button id="remove-12">
remove 12
</button>
So basically you wrap a function inside another function and assign that to a variable that you can register as an event listener, but also unregister as well!

Also try these (IE8 + Chrome. I dont know for FF):
function addEvent(obj, type, fn) {
eval('obj.on'+type+'=fn');
}
function removeEvent(obj, type) {
eval('obj.on'+type+'=null');
}
// Use :
function someFunction (someArg) {alert(someArg);}
var object=document.getElementById('somObject_id') ;
var someArg="Hi there !";
var func=function(){someFunction (someArg)};
// mouseover is inactive
addEvent (object, 'mouseover', func);
// mouseover is now active
addEvent (object, 'mouseover');
// mouseover is inactive
Hope there is no typos :-)

The following answer is correct but the below code is not working in IE8 if suppose you compressed the js file using yuicompressor. (In fact,still most of the US peoples using IE8)
var someVar;
someVar = some_other_function();
alert(someVar);
someObj.addEventListener("click",
function(){
some_function(someVar);
},
false);
So, we can fix the above issue as follows and it works fine in all browsers
var someVar, eventListnerFunc;
someVar = some_other_function();
eventListnerFunc = some_function(someVar);
someObj.addEventListener("click", eventListnerFunc, false);
Hope, it would be useful for some one who is compressing the js file in production environment.
Good Luck!!

var EV = {
ev: '',
fn: '',
elem: '',
add: function () {
this.elem.addEventListener(this.ev, this.fn, false);
}
};
function cons() {
console.log('some what');
}
EV.ev = 'click';
EV.fn = cons;
EV.elem = document.getElementById('body');
EV.add();
//If you want to add one more listener for load event then simply add this two lines of code:
EV.ev = 'load';
EV.add();

The following approach worked well for me. Modified from here.
function callback(theVar) {
return function() {
theVar();
}
}
function some_other_function() {
document.body.innerHTML += "made it.";
}
var someVar = some_other_function;
document.getElementById('button').addEventListener('click', callback(someVar));
<!DOCTYPE html>
<html>
<body>
<button type="button" id="button">Click Me!</button>
</body>
</html>

Since your event listener is 'click', you can:
someObj.setAttribute("onclick", "function(parameter)");

Another workaround is by Using data attributes
function func(){
console.log(this.dataset.someVar);
div.removeEventListener("click", func);
}
var div = document.getElementById("some-div");
div.setAttribute("data-some-var", "hello");
div.addEventListener("click", func);
jsfiddle

The following code worked fine for me (firefox):
for (var i=0; i<3; i++) {
element = new ... // create your element
element.counter = i;
element.addEventListener('click', function(e){
console.log(this.counter);
... // another code with this element
}, false);
}
Output:
0
1
2

You need:
newElem.addEventListener('click', {
handleEvent: function (event) {
clickImg(parameter);
}
});

How to detect when an .html() function is called in jQuery?

The problem is simple. I have a massive javascript application. And there are lot of times in the app where I use code which looks something like this -
$('#treat').html(new_data);
....
....
$('#cool').html(some_html_data);
....
....
$('#not_cool').html(ajax_data);
So what I want to do is, everytime this html() function is called I want to execute a set of functions.
function do_these_things_every_time_data_is_loaded_into_a_div()
{
$('select').customSelect();
$('input').changeStyle();
etc.
}
How do I do this? Thank you.

You can use the custom event handlers for that:
$('#treat').html(new_data);
// Trigger the custom event after html change
$('#treat').trigger('custom');
// Custom event handler
$('#treat').on('custom', function( event) {
// do_these_things_every_time_data_is_loaded_into_a_div
alert('Html had changed!');
});
UPDATE
Based on answer over here and with some modifications you can do this:
// create a reference to the old `.html()` function
$.fn.htmlOriginal = $.fn.html;
// redefine the `.html()` function to accept a callback
$.fn.html = function (html, callback) {
// run the old `.html()` function with the first parameter
this.htmlOriginal(html);
// run the callback (if it is defined)
if (typeof callback == "function") {
callback();
}
}
$("#treat").html(new_data, function () {
do_these_things_every_time_data_is_loaded_into_a_div();
});
$("#cool").html(new_data, function () {
do_these_things_every_time_data_is_loaded_into_a_div();
});
Easily maintainable and less code as per your requirements.

You can overwrite the jQuery.fn.html() method, as described in Override jQuery functions
For example, use this:
var oHtml = jQuery.fn.html;
jQuery.fn.html = function(value) {
if(typeof value !== "undefined")
{
jQuery('select').customSelect();
jQuery('input').changeStyle();
}
// Now go back to jQuery's original html()
return oHtml.apply(this, value);
};

When html() is called it usually make the DOM object changes, so you can look for DOM change event handler, it is called whenever your HTML of main page change. I found
Is there a JavaScript/jQuery DOM change listener?
if this help your cause.

You can replace the html function with your own function and then call the function html:
$.fn.html = (function(oldHtml) {
var _oldHtml = oldHtml;
return function(param) {
// your code
alert(param);
return _oldHtml.apply(this, [param]);
};
})($.fn.html);

I have a little script for you. Insert that into your javascript:
//#Author Karl-André Gagnon
$.hook = function(){
$.each(arguments, function(){
var fn = this
if(!$.fn['hooked'+fn]){
$.fn['hooked'+fn] = $.fn[fn];
$.fn[fn] = function(){
var r = $.fn['hooked'+fn].apply(this, arguments);
$(this).trigger(fn, arguments);
return r
}
}
})
}
This allow you to "hook" jQuery function and trigger an event when you call it.
Here how you use it, you first bind the function you want to trigger. In your case, it will be .html():
$.hook('html');
Then you add an event listener with .on. It there is no dynamicly added element, you can use direct binding, else, delegated evets work :
$(document).on('html', '#threat, #cool, #not_cool',function(){
alert('B');
})
The function will launch everytime #threat, #cool or #not_cool are calling .html.
The $.hook plugin is not fully texted, some bug may be here but for your HTML, it work.
Example : http://jsfiddle.net/5svVQ/

How to dynamically assign DOM event and then execute it?

i am trying to execute DOM events within a function that expects the event to handle, such as onmouseover, onclick and so on, by name as a function parameter like so:
...
doSomething(target, 'onmouseover');
doSomething : function(tgt, evt)
{
...
o.evt = function() {
alert(evt);
}
...
}
...
The assignment does not throw any errors, so i guess, it is syntactically correct, but it does also not do the alert. Why?
(Please do not recommend using frameworks. I would like to understand my mistake and how to get this managed.)

You can assign the event dynamically using the [] notation:
Demo
var obj = {
doSomething : function(tgt, evt)
{
tgt[evt] = function() {
alert(evt);
}
}
};
obj.doSomething(document.getElementById("test"), 'onmouseover');

How to pass arguments to addEventListener listener function?

The situation is somewhat like-
var someVar = some_other_function();
someObj.addEventListener("click", function(){
some_function(someVar);
}, false);
The problem is that the value of someVar is not visible inside the listener function of the addEventListener, where it is probably being treated as a new variable.

Why not just get the arguments from the target attribute of the event?
Example:
const someInput = document.querySelector('button');
someInput.addEventListener('click', myFunc, false);
someInput.myParam = 'This is my parameter';
function myFunc(evt)
{
window.alert(evt.currentTarget.myParam);
}
<button class="input">Show parameter</button>
JavaScript is a prototype-oriented language, remember!

There is absolutely nothing wrong with the code you've written. Both some_function and someVar should be accessible, in case they were available in the context where anonymous
function() { some_function(someVar); }
was created.
Check if the alert gives you the value you've been looking for, be sure it will be accessible in the scope of anonymous function (unless you have more code that operates on the same someVar variable next to the call to addEventListener)
var someVar;
someVar = some_other_function();
alert(someVar);
someObj.addEventListener("click", function(){
some_function(someVar);
}, false);

This question is old but I thought I'd offer an alternative using ES5's .bind() - for posterity. :)
function some_func(otherFunc, ev) {
// magic happens
}
someObj.addEventListener("click", some_func.bind(null, some_other_func), false);
Just be aware that you need to set up your listener function with the first param as the argument you're passing into bind (your other function) and the second param is now the event (instead of the first, as it would have been).

Quite and old question but I had the same issue today. Cleanest solution I found is to use the concept of currying.
The code for that:
someObj.addEventListener('click', some_function(someVar));
var some_function = function(someVar) {
return function curried_func(e) {
// do something here
}
}
By naming the curried function it allows you to call Object.removeEventListener to unregister the eventListener at a later execution time.

You can just bind all necessary arguments with 'bind':
root.addEventListener('click', myPrettyHandler.bind(null, event, arg1, ... ));
In this way you'll always get the event, arg1, and other stuff passed to myPrettyHandler.
http://passy.svbtle.com/partial-application-in-javascript-using-bind

nice one line alternative
element.addEventListener('dragstart',(evt) => onDragStart(param1, param2, param3, evt));
function onDragStart(param1, param2, param3, evt) {
//some action...
}

You can add and remove eventlisteners with arguments by declaring a function as a variable.
myaudio.addEventListener('ended',funcName=function(){newSrc(myaudio)},false);
newSrc is the method with myaudio as parameter
funcName is the function name variable
You can remove the listener with
myaudio.removeEventListener('ended',func,false);

Function.prototype.bind() is the way to bind a target function to a particular scope and optionally define the this object within the target function.
someObj.addEventListener("click", some_function.bind(this), false);
Or to capture some of the lexical scope, for example in a loop:
someObj.addEventListener("click", some_function.bind(this, arg1, arg2), false);
Finally, if the this parameter is not needed within the target function:
someObj.addEventListener("click", some_function.bind(null, arg1, arg2), false);

You could pass somevar by value(not by reference) via a javascript feature known as closure:
var someVar='origin';
func = function(v){
console.log(v);
}
document.addEventListener('click',function(someVar){
return function(){func(someVar)}
}(someVar));
someVar='changed'
Or you could write a common wrap function such as wrapEventCallback:
function wrapEventCallback(callback){
var args = Array.prototype.slice.call(arguments, 1);
return function(e){
callback.apply(this, args)
}
}
var someVar='origin';
func = function(v){
console.log(v);
}
document.addEventListener('click',wrapEventCallback(func,someVar))
someVar='changed'
Here wrapEventCallback(func,var1,var2) is like:
func.bind(null, var1,var2)

Here's yet another way (This one works inside for loops):
var someVar = some_other_function();
someObj.addEventListener("click",
function(theVar){
return function(){some_function(theVar)};
}(someVar),
false);

someVar value should be accessible only in some_function() context, not from listener's.
If you like to have it within listener, you must do something like:
someObj.addEventListener("click",
function(){
var newVar = someVar;
some_function(someVar);
},
false);
and use newVar instead.
The other way is to return someVar value from some_function() for using it further in listener (as a new local var):
var someVar = some_function(someVar);

one easy way to execute that may be this
window.addEventListener('click', (e) => functionHandler(e, ...args));
Works for me.

$form.addEventListener('submit', save.bind(null, data, keyword, $name.value, myStemComment));
function save(data, keyword, name, comment, event) {
This is how I got event passed properly.

Use
el.addEventListener('click',
function(){
// this will give you the id value
alert(this.id);
},
false);
And if you want to pass any custom value into this anonymous function then the easiest way to do it is
// this will dynamically create property a property
// you can create anything like el.<your variable>
el.myvalue = "hello world";
el.addEventListener('click',
function(){
//this will show you the myvalue
alert(el.myvalue);
// this will give you the id value
alert(this.id);
},
false);
Works perfectly in my project. Hope this will help

If I'm not mistaken using calling the function with bind actually creates a new function that is returned by the bind method. This will cause you problems later or if you would like to remove the event listener, as it's basically like an anonymous function:
// Possible:
function myCallback() { /* code here */ }
someObject.addEventListener('event', myCallback);
someObject.removeEventListener('event', myCallback);
// Not Possible:
function myCallback() { /* code here */ }
someObject.addEventListener('event', function() { myCallback });
someObject.removeEventListener('event', /* can't remove anonymous function */);
So take that in mind.
If you are using ES6 you could do the same as suggested but a bit cleaner:
someObject.addEventListener('event', () => myCallback(params));

One way is doing this with an outer function:
elem.addEventListener('click', (function(numCopy) {
return function() {
alert(numCopy)
};
})(num));
This method of wrapping an anonymous function in parentheses and calling it right away is called an IIFE (Immediately-Invoked Function Expression)
You can check an example with two parameters in http://codepen.io/froucher/pen/BoWwgz.
catimg.addEventListener('click', (function(c, i){
return function() {
c.meows++;
i.textContent = c.name + '\'s meows are: ' + c.meows;
}
})(cat, catmeows));

In 2019, lots of api changes, the best answer no longer works, without fix bug.
share some working code.
Inspired by all above answer.
button_element = document.getElementById('your-button')
button_element.setAttribute('your-parameter-name',your-parameter-value);
button_element.addEventListener('click', your_function);
function your_function(event)
{
//when click print the parameter value
console.log(event.currentTarget.attributes.your-parameter-name.value;)
}

Sending arguments to an eventListener's callback function requires creating an isolated function and passing arguments to that isolated function.
Here's a nice little helper function you can use. Based on "hello world's" example above.)
One thing that is also needed is to maintain a reference to the function so we can remove the listener cleanly.
// Lambda closure chaos.
//
// Send an anonymous function to the listener, but execute it immediately.
// This will cause the arguments are captured, which is useful when running
// within loops.
//
// The anonymous function returns a closure, that will be executed when
// the event triggers. And since the arguments were captured, any vars
// that were sent in will be unique to the function.
function addListenerWithArgs(elem, evt, func, vars){
var f = function(ff, vv){
return (function (){
ff(vv);
});
}(func, vars);
elem.addEventListener(evt, f);
return f;
}
// Usage:
function doSomething(withThis){
console.log("withThis", withThis);
}
// Capture the function so we can remove it later.
var storeFunc = addListenerWithArgs(someElem, "click", doSomething, "foo");
// To remove the listener, use the normal routine:
someElem.removeEventListener("click", storeFunc);

There is a special variable inside all functions: arguments. You can pass your parameters as anonymous parameters and access them (by order) through the arguments variable.
Example:
var someVar = some_other_function();
someObj.addEventListener("click", function(someVar){
some_function(arguments[0]);
}, false);

I was stuck in this as I was using it in a loop for finding elements and adding listner to it. If you're using it in a loop, then this will work perfectly
for (var i = 0; i < states_array.length; i++) {
var link = document.getElementById('apply_'+states_array[i].state_id);
link.my_id = i;
link.addEventListener('click', function(e) {
alert(e.target.my_id);
some_function(states_array[e.target.my_id].css_url);
});
}

I suggest you to do something like that:
var someVar = some_other_function();
someObj.addEventListener("click", (event, param1 = someVar) => {
some_function(param1);
}, false);

The PERFECT SOLUTION for this is to use Closures like this:
function makeSizer(size) {
return function () {
document.body.style.fontSize = `${size}px`;
};
}
//pass parameters here and keep the reference in variables:
const size12 = makeSizer(12);
const size24 = makeSizer(24);
const size36 = makeSizer(36);
document.getElementById('size-12').addEventListener("click", size12);
document.getElementById('size-24').addEventListener("click", size24);
document.getElementById('size-36').addEventListener("click", size36);
document.getElementById('remove-12').addEventListener("click", ()=>{
document.getElementById('size-12').removeEventListener("click", size12);
alert("Now click on 'size 12' button and you will see that there is no event listener any more");
});
test<br/>
<button id="size-12">
size 12
</button>
<button id="size-24">
size 24
</button>
<button id="size-36">
size 36
</button>
<button id="remove-12">
remove 12
</button>
So basically you wrap a function inside another function and assign that to a variable that you can register as an event listener, but also unregister as well!

Also try these (IE8 + Chrome. I dont know for FF):
function addEvent(obj, type, fn) {
eval('obj.on'+type+'=fn');
}
function removeEvent(obj, type) {
eval('obj.on'+type+'=null');
}
// Use :
function someFunction (someArg) {alert(someArg);}
var object=document.getElementById('somObject_id') ;
var someArg="Hi there !";
var func=function(){someFunction (someArg)};
// mouseover is inactive
addEvent (object, 'mouseover', func);
// mouseover is now active
addEvent (object, 'mouseover');
// mouseover is inactive
Hope there is no typos :-)

The following answer is correct but the below code is not working in IE8 if suppose you compressed the js file using yuicompressor. (In fact,still most of the US peoples using IE8)
var someVar;
someVar = some_other_function();
alert(someVar);
someObj.addEventListener("click",
function(){
some_function(someVar);
},
false);
So, we can fix the above issue as follows and it works fine in all browsers
var someVar, eventListnerFunc;
someVar = some_other_function();
eventListnerFunc = some_function(someVar);
someObj.addEventListener("click", eventListnerFunc, false);
Hope, it would be useful for some one who is compressing the js file in production environment.
Good Luck!!

var EV = {
ev: '',
fn: '',
elem: '',
add: function () {
this.elem.addEventListener(this.ev, this.fn, false);
}
};
function cons() {
console.log('some what');
}
EV.ev = 'click';
EV.fn = cons;
EV.elem = document.getElementById('body');
EV.add();
//If you want to add one more listener for load event then simply add this two lines of code:
EV.ev = 'load';
EV.add();

The following approach worked well for me. Modified from here.
function callback(theVar) {
return function() {
theVar();
}
}
function some_other_function() {
document.body.innerHTML += "made it.";
}
var someVar = some_other_function;
document.getElementById('button').addEventListener('click', callback(someVar));
<!DOCTYPE html>
<html>
<body>
<button type="button" id="button">Click Me!</button>
</body>
</html>

Since your event listener is 'click', you can:
someObj.setAttribute("onclick", "function(parameter)");

Another workaround is by Using data attributes
function func(){
console.log(this.dataset.someVar);
div.removeEventListener("click", func);
}
var div = document.getElementById("some-div");
div.setAttribute("data-some-var", "hello");
div.addEventListener("click", func);
jsfiddle

The following code worked fine for me (firefox):
for (var i=0; i<3; i++) {
element = new ... // create your element
element.counter = i;
element.addEventListener('click', function(e){
console.log(this.counter);
... // another code with this element
}, false);
}
Output:
0
1
2

You need:
newElem.addEventListener('click', {
handleEvent: function (event) {
clickImg(parameter);
}
});

Develop Reference

JavaScript is the programming language of the Web.

Function for an event - javascript

function onClickHandler(e){ //Do stuff... } element.onclick = onClickHandler;

I think you are asking how to create a normal function and use it in various ways? function fnName(e) { ... code ... } Can be used in various ways: element.onclick = fnName; fnName(); //Call it however you like?

First you gotta give your function a name. function clickEvent(e) { ... do stuff ... } Then attach it onto the element like this: element.onClick = clickEvent; When the event is triggered, the event will automatically get passed into the function.

You need to write it in the form of: function fnName(e){ ... code ... } and then you can call fnName and pass the variable you need. If your function does not really need the 'e', you can write function fnName(){ ...code... }

you can do this: element.onclick = function(e){ myfunc(); } function myfunc() { ... code }

Related

Probably a really simple thing but I can't seem to pass an argument into my Javascript function [duplicate]

Attaching different eventListeners for each item in for-of-loop [duplicate]

How to detect when an .html() function is called in jQuery?

How to dynamically assign DOM event and then execute it?

How to pass arguments to addEventListener listener function?

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