HTMLScriptElement
HTML <script>
elements expose the HTMLScriptElement
interface, which provides special properties and methods for manipulating the behavior and execution of <script>
elements (beyond the inherited HTMLElement
interface).
JavaScript files should be served with the application/javascript
MIME type, but browsers are lenient and block them only if the script is served with an image type (image/*
), video type (video/*
), audio type (audio/*
), or text/csv
. If the script is blocked, its element receives an error
event; otherwise, it receives a load
event.
Instance properties
Inherits properties from its parent, HTMLElement
.
HTMLScriptElement.type
-
A string representing the MIME type of the script. It reflects the
type
attribute. HTMLScriptElement.src
-
A string representing the URL of an external script. It reflects the
src
attribute. HTMLScriptElement.event
Deprecated-
A string; an obsolete way of registering event handlers on elements in an HTML document.
HTMLScriptElement.charset
Deprecated-
A string representing the character encoding of an external script. It reflects the
charset
attribute. HTMLScriptElement.async
,HTMLScriptElement.defer
-
The
async
anddefer
attributes are boolean attributes that control how the script should be executed. Thedefer
andasync
attributes must not be specified if thesrc
attribute is absent.There are three possible execution modes:
- If the
async
attribute is present, then the script will be executed asynchronously as soon as it downloads. - If the
async
attribute is absent but thedefer
attribute is present, then the script is executed when the page has finished parsing. - If neither attribute is present, then the script is fetched and executed immediately, blocking further parsing of the page.
The
defer
attribute may be specified with theasync
attribute, so legacy browsers that only supportdefer
(and notasync
) fall back to thedefer
behavior instead of the default blocking behavior.Note: The exact processing details for these attributes are complex, involving many different aspects of HTML, and therefore are scattered throughout the specification. These algorithms describe the core ideas, but they rely on the parsing rules for
<script>
start and end tags in HTML, in foreign content, and in XML; the rules for thedocument.write()
method; the handling of scripting; and so on. - If the
HTMLScriptElement.crossOrigin
-
A string reflecting the CORS setting for the script element. For scripts from other origins, this controls if error information will be exposed.
HTMLScriptElement.text
-
A string that joins and returns the contents of all
Text
nodes inside the<script>
element (ignoring other nodes like comments) in tree order. On setting, it acts the same way as thetextContent
IDL attribute.Note: When inserted using the
document.write()
method,<script>
elements execute (typically synchronously), but when inserted usinginnerHTML
orouterHTML
, they do not execute at all. HTMLScriptElement.fetchPriority
Experimental-
An optional string representing a hint given to the browser on how it should prioritize fetching of an external script relative to other external scripts. If this value is provided, it must be one of the possible permitted values:
high
to fetch at a high priority,low
to fetch at a low priority, orauto
to indicate no preference (which is the default). HTMLScriptElement.noModule
-
A boolean value that if true, stops the script's execution in browsers that support ES modules — used to run fallback scripts in older browsers that do not support JavaScript modules.
HTMLScriptElement.referrerPolicy
-
A string that reflects the
referrerPolicy
HTML attribute indicating which referrer to use when fetching the script, and fetches done by that script.
Static methods
HTMLScriptElement.supports()
-
Returns
true
if the browser supports scripts of the specified type andfalse
otherwise. This method provides a simple and unified method for script-related feature detection.
Instance methods
No specific methods; inherits methods from its parent, HTMLElement
.
Events
No specific events; inherits events from its parent, HTMLElement
.
Examples
Dynamically importing scripts
Let's create a function that imports new scripts within a document creating a <script>
node immediately before the <script>
that hosts the following code (through document.currentScript
).
These scripts will be asynchronously executed.
For more details, see the defer
and async
properties.
js
function loadError(oError) {
throw new URIError(`The script ${oError.target.src} didn't load correctly.`);
}
function prefixScript(url, onloadFunction) {
const newScript = document.createElement("script");
newScript.onerror = loadError;
if (onloadFunction) {
newScript.onload = onloadFunction;
}
document.currentScript.parentNode.insertBefore(
newScript,
document.currentScript
);
newScript.src = url;
}
This next function, instead of prepending the new scripts immediately before the document.currentScript
element, appends them as children of the <head>
tag.
js
function loadError(oError) {
throw new URIError(`The script ${oError.target.src} didn't load correctly.`);
}
function affixScriptToHead(url, onloadFunction) {
const newScript = document.createElement("script");
newScript.onerror = loadError;
if (onloadFunction) {
newScript.onload = onloadFunction;
}
document.head.appendChild(newScript);
newScript.src = url;
}
Sample usage:
js
affixScriptToHead("myScript1.js");
affixScriptToHead("myScript2.js", () => {
alert('The script "myScript2.js" has been correctly loaded.');
});
Checking if a script type is supported
HTMLScriptElement.supports()
provides a unified mechanism for checking whether a browser supports particular types of scripts.
The example below shows how to check for module support, using the existence of the noModule
attribute as a fallback.
js
function checkModuleSupport() {
if ("supports" in HTMLScriptElement) {
return HTMLScriptElement.supports("module");
}
return "noModule" in document.createElement("script");
}
Classic scripts are assumed to be supported on all browsers.
Specifications
Specification |
---|
HTML Standard # htmlscriptelement |
Browser compatibility
BCD tables only load in the browser
See also
- HTML
<script>
element - HTML
<noscript>
element document.currentScript
- Web Workers (code snippets similar to scripts but executed in another global context)