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Intro To DOM: Five Most Common DOM Selectors You Should Know


After I learned some basic HTML, CSS and JavaScript, they are finally meet together.

The DOM is Document Object Model, which is the interface between your JavaScript and HTML + CSS.

The concept is that the browser turns every HTML tag into a JavaScript object that we can manipulate. Everything is stored inside of the document object.

We interact with DOM to do things like: game, scrolling effects, drop-down menus, form validation, interactivity, or animations.

The main DOM process is Select an element and then manipulate.

How do we implement that?

The document comes with a lot of methods for selecting elements. There are five most common methods we need to know:

 1. document.getElementById()
2. document.getElementsByClassName()
3. document.getElementsByTagName()
4. document.querySelector()
5. document.querySelectorAll()

All of them are started by document dot. And these five methods have all been added into the document object.

Now I am going to create a simple HTML page and show you how to implement these methods.

In the HTML page, I have one h1, one h2, and three li tags. In the li tags, I have one id named "highlight", and two class values "bolded".

getElementById

It takes a string argument and returns the one element with a matching ID.

var tag = document.getElementById("highlight");



It selects this li that has ID which is the object, and then it returns to us. Moreover, it seems to show us the HTML but the result of this is actually a JavaScript object.

getElementsByClassName

It takes a string argument and returns a list of elements that have a matching class.

 var tags = document.getElementsByClassName("bolded");

It returns a list not an array. And it contains every element on the page that matches the given class name.

getElementsByTagName

It returns a list of all elements of a given tag name like <h1> or <li>.

var tags = getElementsByTagName("li");

querySelector

It returns the first element that matches a given CSS-style selector.

var tag = document.querySelector("#highlight")  // select by ID
var tag = document.querySelector(".bolded")      //select by class

We need to note that in the (), we should write the select name matches CSS selector rule. 

querySelectorAll

It returns a list of elements that matches a given CSS-style selector.

var tags = document.querySelectorAll("li");










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