Element: innerHTML property
The Element
property
innerHTML
gets or sets the HTML or XML markup contained
within the element.
To insert the HTML into the document rather than replace the contents of an element,
use the method insertAdjacentHTML()
.
Value
A string containing the HTML serialization of the element's
descendants. Setting the value of innerHTML
removes all of the element's
descendants and replaces them with nodes constructed by parsing the HTML given in the
string htmlString.
Exceptions
SyntaxError
DOMException
-
Thrown if an attempt was made to set the value of
innerHTML
using a string which is not properly-formed HTML. NoModificationAllowedError
DOMException
-
Thrown if an attempt was made to insert the HTML into a node whose parent is a
Document
.
Usage notes
The innerHTML
property can be used to examine the current HTML source of the page, including any changes that have been made since the page was initially loaded.
Reading the HTML contents of an element
Reading innerHTML
causes the user agent to serialize the HTML or XML fragment comprised of the element's descendants. The resulting string is returned.
js
let contents = myElement.innerHTML;
This lets you look at the HTML markup of the element's content nodes.
Note: The returned HTML or XML fragment is generated based on the current contents of the element, so the markup and formatting of the returned fragment is likely not to match the original page markup.
Replacing the contents of an element
Setting the value of innerHTML
lets you easily replace the existing contents of an element with new content.
Note: This is a security risk if the string to be inserted might contain potentially malicious content.
When inserting user-supplied data you should always consider using Element.setHTML()
instead, in order to sanitize the content before it is inserted.
For example, you can erase the entire contents of a document by clearing the contents of the document's body
attribute:
js
document.body.innerHTML = "";
This example fetches the document's current HTML markup and replaces the "<"
characters with the HTML entity "<"
, thereby essentially converting the HTML into raw text.
This is then wrapped in a <pre>
element.
Then the value of innerHTML
is changed to this new string.
As a result, the document contents are replaced with a display of the page's entire source code.
js
document.documentElement.innerHTML = `<pre>${document.documentElement.innerHTML.replace(
/</g,
"<"
)}</pre>`;
Operational details
What exactly happens when you set value of innerHTML
?
Doing so causes the user agent to follow these steps:
-
The specified value is parsed as HTML or XML (based on the document type),
resulting in a
DocumentFragment
object representing the new set of DOM nodes for the new elements. -
If the element whose contents are being replaced is a
<template>
element, then the<template>
element'scontent
attribute is replaced with the newDocumentFragment
created in step 1. - For all other elements, the element's contents are replaced with the nodes in the new
DocumentFragment
.
Appending HTML to an element
Setting the value of innerHTML
lets you append new contents to the existing one of an element.
For example, we can append a new list item (<li>
) to the existing list (<ul>
):
HTML
html
<ul id="list">
<li><a href="#">Item 1</a></li>
<li><a href="#">Item 2</a></li>
<li><a href="#">Item 3</a></li>
</ul>
JavaScript
js
const list = document.getElementById("list");
list.innerHTML += `<li><a href="#">Item ${list.children.length + 1}</a></li>`;
Please note that using innerHTML
to append HTML elements (e.g. el.innerHTML += "<a href='…'>link</a>"
) will result in the removal of any previously set event listeners.
That is, after you append any HTML element that way you won't be able to listen to the previously set event listeners.
Security considerations
It is not uncommon to see innerHTML
used to insert text into a web page.
There is potential for this to become an attack vector on a site, creating a potential security risk.
js
let name = "John";
// assuming 'el' is an HTML DOM element
el.innerHTML = name; // harmless in this case
// …
name = "<script>alert('I am John in an annoying alert!')</script>";
el.innerHTML = name; // harmless in this case
Although this may look like a cross-site scripting
attack, the result is harmless. HTML specifies that a <script>
tag
inserted with innerHTML
should not execute.
However, there are ways to execute JavaScript without using <script>
elements,
so there is still a security risk whenever you use innerHTML
to set strings over which you have no control.
For example:
js
const name = "<img src='x' onerror='alert(1)'>";
el.innerHTML = name; // shows the alert
For that reason, it is recommended that instead of innerHTML
you use:
Element.setHTML()
to sanitize the text before it is inserted into the DOM.Node.textContent
when inserting plain text, as this inserts it as raw text rather than parsing it as HTML.
Warning: If your project is one that will undergo any form of security review, using innerHTML
most likely will result in your code being rejected.
For example, if you use innerHTML
in a browser extension and submit
the extension to addons.mozilla.org, it may be rejected in the review process.
Please see Safely inserting external content into a page for alternative methods.
Examples
This example uses innerHTML
to create a mechanism for logging messages into a box on a web page.
JavaScript
js
function log(msg) {
const logElem = document.querySelector(".log");
const time = new Date();
const timeStr = time.toLocaleTimeString();
logElem.innerHTML += `${timeStr}: ${msg}<br/>`;
}
log("Logging mouse events inside this container…");
The log()
function creates the log output by getting the current time from a Date
object using
toLocaleTimeString()
, and building a string with the timestamp and the message text.
Then the message is appended to the box with the class "log"
.
We add a second method that logs information about MouseEvent
based events
(such as mousedown
, click
, and mouseenter
):
js
function logEvent(event) {
const msg = `Event <strong>${event.type}</strong> at <em>${event.clientX}, ${event.clientY}</em>`;
log(msg);
}
Then we use this as the event handler for a number of mouse events on the box that contains our log:
js
const boxElem = document.querySelector(".box");
boxElem.addEventListener("mousedown", logEvent);
boxElem.addEventListener("mouseup", logEvent);
boxElem.addEventListener("click", logEvent);
boxElem.addEventListener("mouseenter", logEvent);
boxElem.addEventListener("mouseleave", logEvent);
HTML
The HTML is quite simple for our example.
html
<div class="box">
<div><strong>Log:</strong></div>
<div class="log"></div>
</div>
The <div>
with the class "box"
is just a container for layout purposes, presenting the contents with a box around it.
The <div>
whose class is "log"
is the container for the log text itself.
CSS
The following CSS styles our example content.
css
.box {
width: 600px;
height: 300px;
border: 1px solid black;
padding: 2px 4px;
overflow-y: scroll;
overflow-x: auto;
}
.log {
margin-top: 8px;
font-family: monospace;
}
Result
The resulting content looks like this. You can see output into the log by moving the mouse in and out of the box, clicking in it, and so forth.
Specifications
Specification |
---|
DOM Parsing and Serialization # dom-innerhtml-innerhtml |
Browser compatibility
BCD tables only load in the browser
See also
Node.textContent
andHTMLElement.innerText
Element.insertAdjacentHTML()
Element.outerHTML
Element.setHTML
- Parsing HTML or XML into a DOM tree:
DOMParser
- Serializing a DOM tree into an XML string:
XMLSerializer