Finding HTML Elements
Often, with JavaScript, you want to manipulate HTML elements.
To do so, you have to find the elements first. There are several ways to do this:
- Finding HTML elements by id
- Finding HTML elements by tag name
- Finding HTML elements by class name
- Finding HTML elements by CSS selectors
- Finding HTML elements by HTML object collections
Finding HTML Element by Id
The easiest way to find an HTML element in the DOM, is by using the element id.
This example finds the element with id="intro":
Example
const element = document.getElementById("intro");
If the element is found, the method will return the element as an object (in element).
If the element is not found, element will contain null.
Finding HTML Elements by Tag Name
This example finds all <p> elements:
Example
const element = document.getElementsByTagName("p");
This example finds the element with id="main", and then finds all <p> elements inside "main":
Example
const x = document.getElementById("main");
const y = x.getElementsByTagName("p");
Finding HTML Elements by Class Name
If you want to find all HTML elements with the same class name, use getElementsByClassName().
This example returns a list of all elements with class="intro".
Example
const x = document.getElementsByClassName("intro");
Finding HTML Elements by CSS Selectors
The querySelector() Method
Example
<html>
<body>
<p class="demo"></p>
<script>
// Access a paragraph Element
const myPara = document.querySelector(".demo");
// Change the content of the Element
myPara.innerHTML = "Hello World!";
</script>
</body>
</html>
The querySelectorAll() Method
Example
<html>
<body>
<p class="demo">One</p>
<p class="demo">Two</p>
<script>
// Access a paragraph Element
const myItems = document.querySelectorAll(".demo");
// Change the content of the Element
myItems[0].innerHTML = "First";
</script>
</body>
</html>
Common Mistakes
- Using
#in getElementById(): Wrong: "#demo" - Forgetting that querySelector() returns only the first match
If you want to find all HTML elements that match a specified CSS selector (id, class names, types, attributes, values of attributes, etc), use the querySelectorAll() method.
This example returns a list of all <p> elements with class="intro".
Example
const x = document.querySelectorAll("p.intro");
Finding HTML Elements by HTML Object Collections
This example finds the form element with id="frm1", in the forms collection, and displays all element values:
Example
const x = document.forms["frm1"];
let text = "";
for (let i = 0; i < x.length; i++) {
text += x.elements[i].value + "<br>";
}
document.getElementById("demo").innerHTML = text;
The following HTML objects (and object collections) are also accessible:
