Eventlisteners and its use
EventListener in Javascript
An Eventlistener is a method in JavaScript that attaches an event to to an element.
The listener is programed to start an event when the input or signaling the event handler.
Syntax:-
element.addEventListener(event, function, useCapture);
some EventListeners are :-
onload //when the page loads
onclick //when a user clicks something
onmouseover //when a user mouses over something
onmouseup //when a user mouses down from something
onmousedown //when a user mouses up from something
onmouseout //when a user mouses out something
onfocus //when a user puts the cursor in a form field
onblur //When a user leaves a form field
```Events in javascript
// On clicking button this function works
1
2
3
4
5
function clicked() {
console.log("The button was clicked.")
}
// On loading page this function works
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
window.onload =function(){
console.log("The document was loaded.");
}
let ids = document.getElementById("firstcontainer")
ids.addEventListener('click', function(){
console.log("clicked on container");
})
ids.addEventListener('mouseout', function(){
console.log("mouseout container");
})
ids.addEventListener('mouseover', function(){
console.log("mouse on container");
})
ids.addEventListener('mouseup', function(){
console.log("mouseup clicked on container");
})
ids.addEventListener('mousedown', function(){
console.log("mousedown clicked on container");
})
1
2
3
4
5
6
7
8
9
10
11
You can add many event handlers to one element.
## The removeEventListener() method
body.removeEventListener(‘click’, bodyClickHandler);
// on each click of the page, you will no longer see a message
```
we use the removeEventListener method correctly. This time when a click event occurs, removeEventListener will remove the function bodyClickHandler which effectively eliminates the listener, and no clicks will generate a message.