PerformanceElementTiming: toJSON() method
Limited availability
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Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.
The toJSON() method of the PerformanceElementTiming interface is a serializer; it returns a JSON representation of the PerformanceElementTiming object.
Syntax
toJSON()
Parameters
None.
Return value
A JSON object that is the serialization of the PerformanceElementTiming object.
The JSON doesn't contain the element property because it is of type Element, which doesn't provide a toJSON() operation. The id of the element is provided, though.
Examples
Using the toJSON method
In this example, calling entry.toJSON() returns a JSON representation of the PerformanceElementTiming object, with the information about the image element.
<img
src="image.jpg"
alt="a nice image"
elementtiming="big-image"
id="myImage" />
const observer = new PerformanceObserver((list) => {
list.getEntries().forEach((entry) => {
if (entry.identifier === "big-image") {
console.log(entry.toJSON());
}
});
});
observer.observe({ type: "element", buffered: true });
This would log a JSON object like so:
{
"name": "image-paint",
"entryType": "element",
"startTime": 670894.1000000238,
"duration": 0,
"renderTime": 0,
"loadTime": 670894.1000000238,
"intersectionRect": {
"x": 299,
"y": 76,
"width": 135,
"height": 155,
"top": 76,
"right": 434,
"bottom": 231,
"left": 299
},
"identifier": "big-image",
"naturalWidth": 135,
"naturalHeight": 155,
"id": "myImage",
"url": "https://en.wikipedia.org/static/images/project-logos/enwiki.png"
}
To get a JSON string, you can use JSON.stringify(entry) directly; it will call toJSON() automatically.
Specifications
| Specification |
|---|
| Element Timing API # dom-performanceelementtiming-tojson |
Browser compatibility
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