Analysis of the conversion and difference between jQuery's DOM objects and jQuery objects_jquery

This article analyzes the conversion and difference between DOM objects and jQuery objects with examples. Share it with everyone for your reference. The specific analysis is as follows:

jQuery Hello World program:

Comparison of $(document).ready and window.onload

First look at window.onload:

Copy code The code is as follows:

window.onload = sayHello;
window.onload = sayWorld;

function sayHello() {
alert("Hello");
}
function sayWorld() {
​ alert("World");
}

The latter method will overwrite the previous method, that is, only one bubble will be displayed in the end, the one of World.

If $(document).ready is used, the methods will be concatenated, that is, the Hello alert will be displayed first, and then the World alert will be displayed.

Copy code The code is as follows:

$(document).ready(sayHello);
$(document).ready(sayWorld);

function sayHello() {
alert("Hello");
}
function sayWorld() {
​ alert("World");
}

This way you can associate multiple methods.
Another small difference is that the execution of the ready method will be slightly earlier. width.onload will wait for the DOM to be ready and all binding to be completed, while ready can only prepare the DOM, and other work may not be done yet.

Example: Attach onclick event to each hyperlink object

First, add multiple hyperlink objects to the body:

Copy code The code is as follows:

test1

test2

test3

test4

To add an onclick event to each object, there are many methods:
First of all, you can write the onclick attribute in each a tag;
Secondly, you can use window.onload to add a method to obtain all tags and add events uniformly, as follows:

Copy code The code is as follows:

window.onload = function () {
var myLinks = document.getElementsByTagName("a");
for(var i = 0; i < myLinks.length; i){
myLinks[i].onclick = function(){
alert("Hello link: " i);
}
}
}

Note that I made a mistake here. I originally thought that the number of alerts would increase, but the actual result was that each alert was 4.
This is because js does not have a block-level scope , and the variable i refers to the one in for, which becomes 4 after the loop. In other words, the value of i is only taken when the onclick event occurs, of course. It’s 4.

Use jQuery to implement this function below:

Copy code The code is as follows:

$(document).ready(function () {
$("a").click(function () {
alert("Hello link from jQuery!");
});
});

The $() symbol in jQuery will get all the appropriate elements in the page.
So the above code implies the traversal process and adds an event processing function to each element.
The click method is a method provided by the jQuery object.
onclick is a property of the DOM object.
Many attributes in DOM become methods in jQuery.

Mutual conversion and difference between DOM objects and jQuery objects

Look at an example, first add a p tag:

Copy code The code is as follows:

Click Me!

First get a DOM object, and then convert it into a jQuery object:

Copy code The code is as follows:

//Part 1: DOM --> jQuery
//DOM object:
var pElement = document.getElementsByTagName("p")[0];
alert("DOM pElement: " pElement.innerHTML);
//Convert DOM object to jQuery object:
var pElementjQuery = $(pElement);
alert("jQuery pElementjQuery: " pElementjQuery.html());

You can also obtain a jQuery object first and then convert it into a DOM object:

Copy code The code is as follows:

//Part 2: jQuery --> DOM
//jQuery object array:
var clickMejQuery = $("#clickMe");
//Convert jQuery object to DOM object (2 ways):
//way 1:
var domClickMe1 = clickMejQuery[0];
alert("dom1: " domClickMe1.innerHTML);

//way 2:
var domClickMe2 = clickMejQuery.get(0);
alert("dom2: " domClickMe2.innerHTML);

Note again: $() in jQuery obtains an array of all elements that meet the conditions.

Small summary:

$("string") will return an array of all elements that meet the conditions, where:
The string starts with #, indicating id;
The string starts with ., indicating the CSS class name;
If the above two situations are not the case, change the string to represent the tag name.

$(DOM object) can get a jQuery object.

I hope this article will be helpful to everyone’s jQuery programming.