Why do you need AddEventListener?
Let's take a look at a fragment:
HTML code
<div id= "box" > Chasing the Dream Child </div>
With on code
Window.onload = function () {
var box = document.getElementById ("box");
Box.onclick = function () {
Console.log ("I am Box1");
}
Box.onclick = function () {
box.style.fontSize = "18px";
Console.log ("I am Box2");
}
Run Result: "I am Box2"
You see, the second onclick covers the first onclick, although most of the time we use on to get the results we want, but sometimes we need to execute multiple identical events, and obviously if we don't do what we want with on, then don't guess, you must know, yes! AddEventListener can bind the same event multiple times and will not overwrite the previous event.
Using the AddEventListener code
Window.onload = function () {
var box = document.getElementById ("box");
Box.addeventlistener ("click", Function () {
Console.log ("I am Box1");
})
Box.addeventlistener ("click", Function () {
Console.log ("I am Box2")
}
Run Result: I'm box1,
I'm box2.
Addeventlistenert method The first parameter fills in the event name, note that you do not need to write on, the second argument can be a function, and the third parameter refers to handling the event handler in the bubbling or capturing phase, if true represents capture-phase processing. If False represents bubbling phase processing, the third argument can be omitted, and most cases do not require a third parameter, not a third argument default false
Use of the third parameter
Sometimes this is the case.
<body>
<div id= "box" >
<div id= "Child" ></div>
</div>
</body>
If I add the Click event to box, what if I click on the box, but if I click the child element, how does it perform? (Order of execution)
Box.addeventlistener ("click", Function () {
console.log ("box");
})
Child.addeventlistener ("click", Function () {
console.log ("Child");
})
Result of execution:
child
Box
In other words, the default event events are performed in the order in which the event bubbles are executed.
If the third argument writes True, it is performed in the order in which the events are captured.
Box.addeventlistener ("click", Function () {
console.log ("box"),
},true)
Child.addeventlistener (" Click, function () {
console.log ("Child");
})
Result of execution:
box
Child
Event Bubbling Execution Process:
Start bubbling up from the most specific element (the element you clicked), take our case above to say its order is: Child->box
Event Capture Execution Process:
From the least specific element (the outermost box) began to bubble inside, take our case above the order is: Box->child
The above comprehensive understanding of the difference between AddEventListener and on is small series to share all the content, hope to give you a reference, but also hope that we support the cloud habitat community.
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