DOM: Basic DOM Methods

Here are the essential Document Object Model methods. Learn to use these and you will know 99% of practical DOM use.

Get Elements

syntax	meaning
document. getElementById (id)	Return a (none-live) element object or null.
document. getElementsByTagName (tag_name)	Return a live HTMLCollection.
document. getElementsByClassName (class_value)	Return a live HTMLCollection.
document. querySelector (css_selector)	Return a non-live HTMLCollection of the first element that matches.
document. querySelectorAll (css_selector)	Return a non-live HTMLCollection.

For examples, see:

DOM: Get Elements by ID, Tag, Name, Class, CSS Selector

Element Attribute

Properties for Working with Element's Attributes

syntax	meaning
node.hasAttribute (attr)	Return true or false. This is especially useful for “boolean attributes” that doesn't have value, such as the attribute checked of input tag for checkboxes.
node.getAttribute (attr)	Return the value of element's attribute attr. If doesn't exist, returns null. The attr is any of {"id", "href", …}. [see DOM: Get Element's Attribute Value]
node.setAttribute (attr, val)	Set the value of the attribute named attr to value val. If the attribute does not exist, it will be created. Return undefined. [see DOM: Set Element's Attribute Value]
node.removeAttribute (attr)	Remove the attribute. No error if attribute doesn't exist. Return undefined. [see DOM: Remove Element's Attribute Value]
node.attributes	Get all attributes. Return a live Array-Like Object.

For HTML element's standard attributes, you can use a property directly.

Get/Set Standard Attributes by Properties

syntax	meaning
html_element.attribute_name	Return element's attribute's value, or undefined if it doesn't exist.
html_element.attribute_name = value	Set a element's attribute. Return value. If attribute_name is not a standard html attribute, it's not added.

const x = document.getElementsByTagName("a")[0];

x.getAttribute("href");
// is equivalent to
x.href

Using property does not work with XML such as stroke="…" from SVG, or non-standard attributes such as data-xyz="…" from HTML5 Custom Data Attribute.

“class” Attribute

For the class attribute, there's more useful methods.

see DOM: List/Add/Remove Class Attribute

“style” Attribute

For the style attribute, you can use HTML Element properties.

Note, HTML Element properties may not work with XML, e.g. SVG's stroke. [see SVG: Specifying Styles]

syntax	meaning
node.style.css_attribute	Return the attribute value, or undefined if it doesn't exist.
node.style.css_attribute=value	Set css attribute. Return value. If attribute is not a standard css attribute, it's not added.

Example: DOM: Change CSS

Get Node {Type, Name, Value}

HTML element is a node. But node also includes white spaces between elements, comments, doctype, and arbitrary XML tags.

syntax	meaning
node.nodeType	A integer representing the type of the node node (1 means HTML element, 3 means text node).
node.nodeName	The name of the node node (either the name of tag (For example, P, DIV, SPAN, …) or "#text")
node.nodeValue	The text value of text node or attribute node. Else, null.

[see DOM: Node Type, Node Name, Node Value]

Navigate Nodes

syntax	meaning
node.previousSibling	Return null if none.
node.nextSibling	Return null if none.
node.firstChild	Return null if none.
node.lastChild	Return null if none.
node.parentNode	Return null if none.

syntax	meaning
node.hasChildNodes()	Return true or false.
node.childNodes	Return read-only live object NodeList. If no child, the object has length 0.
node.children	Return read-only live object HTMLCollection. Value is all non-whitespace children of node.

[see DOM: Navigate DOM Tree]

Create New Nodes

syntax	meaning
document. createElement (tag_name)	Create a new tag_name element node. Return it.
document. createTextNode (str)	Create a new text node with the node value of string str.
node.cloneNode(true)	Return a copy of node, including all child nodes if argument is true.
node.innerHTML	The content of node as string. You can read or set this value. [see DOM: Difference Between textContent, innerHTML, innerText, nodeValue]

[see DOM: Create/Insert HTML Element]

{Insert, Remove, Replace} Nodes

syntax	meaning
node.insertAdjacentElement(position, new_node)	[see DOM: .insertAdjacentElement]

syntax	meaning
p_node.appendChild (new_node)	Returns the argument new_node. [see DOM: .appendChild]
p_node.insertBefore (new_node, nodeX)	Inserts new_node as a new child of p_node before nodeX.
p_node.removeChild (old_node)	Removes the child old_node from p_node.
p_node.replaceChild (new_node, old_node)	Replaces the child node old_node of p_node with new_node. If new_node is in the same doc, it'll also be removed.

Examples:

• DOM: Create/Insert HTML Element
• DOM: Remove HTML Element
• DOM: Insert After a Element

Change Element's Text Content

There are 3 ways to change a element's content.

1. Treat it as a innerHTML, and use property innerHTML . This is for HTML (not XML), works in all browsers.
2. Treat it as a text content, and use property textContent . This works well if the content is text and contains no HTML. (if you set value to "<b>bold text</b>", the text won't be bold.)
3. Treat it as a DOM tree node, and use property nodeValue. This is the most general, and works with XML too.

Example: DOM: Change Element's Content

Detail: DOM: Difference Between textContent, innerHTML, innerText, nodeValue

{Add, Remove} Event Handler

syntax	meaning
node.addEventListener (event, ƒ, false)	Add the function ƒ to the event event
node.removeEventListener (event, ƒ …)	Remove the function ƒ that was attached to the event event

[see DOM: Add/Remove Event Handler]