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14.13 DOM Collections

The getElementsByTagName() method returns an HTMLCollection object.
An HTMLCollection object is an array-like list (collection) of HTML elements.
The following code selects all <p> elements in a document:

Example 1: JS HTML DOM Collections

var x = document.getElementsByTagName("p");

The elements in the collection can be accessed by an index number.
To access the second <p> element you can write:

y = x[1];

Note: The index starts at 0.

HTML HTMLCollection Length

The length property defines the number of elements in an HTMLCollection:

Example 2: JS HTML DOM Collections - HTMLCollection Length part 1

var myCollection = document.getElementsByTagName("p");
document.getElementById("demo").innerHTML = myCollection.length;

Example explained:
1. Create a collection of all <p> elements
2. Display the length of the collection
The length property is useful when you want to loop through the elements in a collection:

Example 3: JS HTML DOM Collections - HTMLCollection Length part 2

Change the background color of all <p> elements:

var myCollection = document.getElementsByTagName("p");
var i;
for (i = 0; i < myCollection.length; i++) {
  myCollection[i].style.color = "red";
}

An HTMLCollection is NOT an array!
An HTMLCollection may look like an array, but it is not.
You can loop through the list and refer to the elements with a number (just like an array).
However, you cannot use array methods like valueOf(), pop(), push(), or join() on an HTMLCollection.

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Module 14. JS HTML DOM

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Example files created in this module:
HTML DOM Methods JS HTML DOM - Finding HTML Element by Id JS HTML DOM - Finding HTML Elements by Tag Name part 1 JS HTML DOM - Finding HTML Elements by Tag Name part 2 JS HTML DOM - Finding HTML Elements by Class Name JS HTML DOM - Finding HTML Elements by CSS Selectors JS HTML DOM - Finding HTML Elements by HTML document.forms JS Changing HTML Content part 1 JS Changing HTML Content part 2 JS HTML DOM - Changing the Value of an Attribute JS HTML DOM - Dynamic HTML content JS HTML DOM - document.write() JS Validation - HTML Form Example part 1 JS Validation - HTML Form Example part 2 JS HTML DOM - Changing the HTML style JS HTML DOM - Changing the HTML style Using Events My first JS animation part 1 My first JS animation part 2 JS HTML Events - The onclick Attribute part 1 JS HTML Events - The onclick Attribute part 2 JS HTML Events - The onclick Attribute part 3 JS HTML Events - The onclick Attribute part 4 JS HTML Events - The onload Attribute JS addEventListener() part 1 JS addEventListener() part 2 JS addEventListener() part 3 JS addEventListener() part 4 JS addEventListener() part 5 JS addEventListener() part 6 JS addEventListener() part 7 JS addEventListener() part 8 JS removeEventListener() JS HTML Child Nodes and Node Values part 1 JS HTML Child Nodes and Node Values part 2 JS HTML Child Nodes and Node Values part 3 JS HTMLDOM - DOM Root Nodes part 1 JS HTMLDOM - DOM Root Nodes part 2 JS HTMLDOM - The nodeName Property JS HTMLDOM - The nodeType Property JS HTML DOM - Creating New HTML Elements (Nodes) JS HTML DOM - Creating new HTML Elements - insertBefore() JS HTML DOM - Removing Existing HTML Elements JS HTML DOM - Remove Child Element JS HTML DOM - Replacing an HTML Elements JS HTML DOM Collections JS HTML DOM Collections - HTMLCollection Length par 1 JS HTML DOM Collections - HTMLCollection Length part 2 JS HTML DOM - DOM Node Lists JS HTML DOM - DOM Node List Length part 1 JS HTML DOM - DOM Node List Length part 2