The supports() static method of the HTMLScriptElement interface provides a simple and consistent method to feature-detect what types of scripts are supported by the user agent.

The method is expected to return true for classic and module scripts, which are supported by most modern browsers.

type

A string literal that indicates the type of script for which support is to be checked. Supported values are case sensitive, and include:

"classic"

Test if classic scripts are supported. "Classic" scripts are the normal/traditional JavaScript files that predate module scripts.

"module"

Test if module scripts are supported.

"importmap"

Test if import maps are supported.

"speculationrules"

Test if speculation rules are supported and enabled.

Any other value will cause the method to return false.

Returns true if the indicated script type is supported and false otherwise.

The code below shows how to check if HTMLScriptElement.supports() is defined, and if so, to use it to test whether particular types of scripts are supported.

const log = document.getElementById("log");

function checkSupport(type) {
  const result = HTMLScriptElement.supports(type) ? "true" : "false";
  log.textContent += `HTMLScriptElement.supports('${type}') is ${result}\n`;
}

if (typeof HTMLScriptElement.supports === "undefined") {
  log.textContent = "HTMLScriptElement.supports() method is not supported";
} else {
  // Check if various script types are supported
  checkSupport("module");
  checkSupport("classic");
  checkSupport("importmap");
  checkSupport("speculationrules");
  // Any other value will cause the method to return false
  checkSupport("anything else");
}

• HTMLScriptElement
• <script>
• JavaScript modules
• Worker constructor