The replace() method of the CSSStyleSheet interface asynchronously replaces the content of the stylesheet with the content passed into it. The method returns a promise that resolves with the CSSStyleSheet object.

The replace() and CSSStyleSheet.replaceSync() methods can only be used on a stylesheet created with the CSSStyleSheet() constructor.

text

A string containing the style rules to replace the content of the stylesheet. If the string does not contain a parseable list of rules, then the value will be set to an empty string.

Note: If any of the rules passed in text are an external stylesheet imported with the @import rule, those rules will be removed, and a warning printed to the console.

A Promise that resolves with the CSSStyleSheet.

NotAllowedError DOMException

Thrown if one of these two conditions is met:

• The stylesheet was not created using the CSSStyleSheet() constructor.
• The stylesheet is flagged as unmodifiable.

In the following example a new stylesheet is created and two CSS rules are added using replace(). The first rule is then printed to the console, which will return: body { font-size: 1.4em; }

const stylesheet = new CSSStyleSheet();

stylesheet
  .replace("body { font-size: 1.4em; } p { color: red; }")
  .then(() => {
    console.log(stylesheet.cssRules[0].cssText);
  })
  .catch((err) => {
    console.error("Failed to replace styles:", err);
  });

• Constructable Stylesheets (web.dev)
• Using the Shadow DOM