Limited availability
Note: This feature is available in Web Workers.
Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.
The contentType read-only property of the PerformanceResourceTiming interface is a string indicating the content type of the fetched resource, formatted as a MIME type and subtype separated by a forward slash.
The content type is a minimized and "standardized" version of the MIME type that is extracted from the Content-Type HTTP header sent in the resource's fetch response. For JavaScript, JSON, SVG, and XML, the MIME type is replaced by a representative MIME type/subtype string. Other types supported by the browser are represented by the MIME type/subtype string in the header (other information in the header is discarded).
A string indicating the MIME type "essence" of the content. This may be one of the following values:
text/javascript
JavaScript content.
application/json
JSON content.
image/svg+xml
SVG content.
application/xml
XML content (other than SVG).
Any other MIME type/subtype supported by the user agent.
"" (empty string)
Returned for MIME types that are not supported by the browser, or if the resource fetch failed due to CORS checks.
The contentType property can be used to get specific resource timing entries only; for example, only those related to scripts.
The following example uses a PerformanceObserver to notify of new resource performance entries as they are recorded in the browser's performance timeline. The buffered option is used for accessing entries from before the observer creation.
const observer = new PerformanceObserver((list) => {
const javascriptResources = list
.getEntries()
.filter((entry) => entry.contentType === "text/javascript");
console.log(javascriptResources);
});
observer.observe({ type: "resource", buffered: true });
The following example uses Performance.getEntriesByType(), which only shows resource performance entries present in the browser's performance timeline at the time you call the method.
const scripts = performance
.getEntriesByType("resource")
.filter((entry) => entry.contentType === "text/javascript");
console.log(scripts);
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