Element: innerHTML property

{{APIRef("DOM")}}

[!WARNING] This property parses its input as HTML, writing the result into the DOM. APIs like this are known as injection sinks, and are potentially a vector for cross-site-scripting (XSS) attacks, if the input originally came from an attacker.

You can mitigate this risk by always assigning TrustedHTML objects instead of strings and enforcing trusted types. See Security considerations for more information.

The innerHTML property of the {{domxref("Element")}} interface gets or sets the HTML or XML markup contained within the element, omitting any {{glossary("shadow tree", "shadow roots")}} in both cases.

To insert the HTML into the document rather than replace the contents of an element, use the method {{domxref("Element.insertAdjacentHTML", "insertAdjacentHTML()")}} .

Value

Getting the property returns a string containing the HTML serialization of the element’s descendants.

Setting the property accepts either a {{domxref("TrustedHTML")}} object or a string. It parses this value as HTML and replaces all the element’s descendants with the result. When set to the null value, that null value is converted to the empty string (""), so elt.innerHTML = null is equivalent to elt.innerHTML = "".

Exceptions

SyntaxError {{domxref("DOMException")}}
- : Thrown if an attempt was made to set the value of innerHTML using a string which is not properly-formed HTML.
TypeError
- : Thrown if the property is set to a string when Trusted Types are enforced by a CSP and no default policy is defined.
NoModificationAllowedError {{domxref("DOMException")}}
- : Thrown if an attempt was made to insert the HTML into a node whose parent is a {{domxref("Document")}} .

Description

innerHTML gets a serialization of the nested child DOM elements within the element, or sets HTML or XML that should be parsed to replace the DOM tree within the element.

Note that some browsers serialize the < and > characters as < and > when they appear in attribute values (see Browser compatibility). This is to prevent a potential security vulnerability (mutation XSS) in which an attacker can craft input that bypasses a sanitization function, enabling a cross-site scripting (XSS) attack.

Shadow DOM considerations

The serialization of the DOM tree read from the property does not include {{glossary("shadow tree", "shadow roots")}} — if you want to get a HTML string that includes shadow roots, you must instead use the {{domxref("Element.getHTML()")}} or {{domxref("ShadowRoot.getHTML()")}} methods.

Similarly, when setting element content using innerHTML, the HTML string is parsed into DOM elements that do not contain shadow roots. So for example <template> is parsed into as {{domxref("HTMLTemplateElement")}} , whether or not the shadowrootmode attribute is specified. In order to set an element’s contents from an HTML string that includes declarative shadow roots, you must instead use {{domxref("Element.setHTMLUnsafe()")}} or {{domxref("ShadowRoot.setHTMLUnsafe()")}} .

Security considerations

The innerHTML property is probably the most common vector for Cross-site-scripting (XSS) attacks, where potentially unsafe strings provided by a user are injected into the DOM without first being sanitized. While the property does prevent {{HTMLElement("script")}} elements from executing when they are injected, it is susceptible to many other ways that attackers can craft HTML to run malicious JavaScript. For example, the following example would execute the code in the error event handler, because the {{htmlelement("img")}} src value is not a valid image URL:

const name = "<img src='x' onerror='alert(1)'>";
el.innerHTML = name; // shows the alert

You can mitigate these issues by always assigning {{domxref("TrustedHTML")}} objects instead of strings, and enforcing trusted type using the require-trusted-types-for CSP directive. This ensures that the input is passed through a transformation function, which has the chance to sanitize the input to remove potentially dangerous markup before it is injected.

[!NOTE] {{domxref("Node.textContent")}} should be used when you know that the user provided content should be plain text. This prevents it being parsed as HTML.

Examples

Reading the HTML contents of an element

Reading innerHTML causes the user agent to serialize the element’s descendants.

Given the following HTML:

<div id="example">
  <p>My name is Joe</p>
</div>

You can get and log the markup for the contents of the outer {{htmlelement("div")}} as shown:

const myElement = document.querySelector("#example");
const contents = myElement.innerHTML;
console.log(contents); // "\n  <p>My name is Joe</p>\n"

Replacing the contents of an element

In this example we’ll replace an element’s DOM by assigning HTML to the element’s innerHTML property. To mitigate the risk of XSS, we’ll first create a TrustedHTML object from the string containing the HTML, and then assign that object to innerHTML.

Trusted types are not yet supported on all browsers, so first we define the trusted types tinyfill. This acts as a transparent replacement for the trusted types JavaScript API:

if (typeof trustedTypes === "undefined")
  trustedTypes = { createPolicy: (n, rules) => rules };

Next we create a {{domxref("TrustedTypePolicy")}} that defines a {{domxref("TrustedTypePolicy/createHTML", "createHTML()")}} for transforming an input string into {{domxref("TrustedHTML")}} instances. Commonly implementations of createHTML() use a library such as DOMPurify to sanitize the input as shown below:

const policy = trustedTypes.createPolicy("my-policy", {
  createHTML: (input) => DOMPurify.sanitize(input),
});

Then we use this policy object to create a TrustedHTML object from the potentially unsafe input string, and assign the result to the element:

// The potentially malicious string
const untrustedString = "<p>I might be XSS</p><img src='x' onerror='alert(1)'>";

// Create a TrustedHTML instance using the policy
const trustedHTML = policy.createHTML(untrustedString);

// Inject the TrustedHTML (which contains a trusted string)
const element = document.querySelector("#container");
element.innerHTML = trustedHTML;

[!WARNING] While you can directly assign a string to innerHTML this is a security risk if the string to be inserted might contain potentially malicious content. You should use TrustedHTML to ensure that the content is sanitized before it is inserted, and you should set a CSP header to enforce trusted types.

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

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