LayoutShift: toJSON() method
Limited availability
This feature is not Baseline because it does not work in some of the most widely-used browsers.
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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 LayoutShift interface returns a JSON-serializable plain object representing the LayoutShift object.
The method is automatically called by JSON.stringify() when a LayoutShift object is encountered during JSON serialization.
Syntax
toJSON()
Parameters
None.
Return value
A JSON-serializable plain object containing the following properties:
Each property's value is copied as-is. When the returned object is passed to JSON.stringify(), the objects in the sources array are further serialized using LayoutShiftAttribution.toJSON().
Examples
Calling toJSON() directly
This example obtains a LayoutShift object. Calling toJSON() directly returns a plain object. Its properties have the same values as the corresponding properties of the original object.
const observer = new PerformanceObserver((list) => {
list.getEntries().forEach((entry) => {
const json = entry.toJSON();
console.log(json); // A plain object
console.log(typeof json); // "object"
console.log(json.value); // Same value as entry.value
});
});
observer.observe({ type: "layout-shift", buffered: true });
Serializing to a JSON string
Within the callback from the previous example, the same object can be serialized using JSON.stringify(), which calls the toJSON() method automatically.
console.log(JSON.stringify(entry));
This would log a JSON string like so (formatted for readability):
{
"name": "",
"entryType": "layout-shift",
"startTime": 246.5,
"duration": 0,
"navigationId": 2463,
"value": 0.0071167845054842215,
"hadRecentInput": false,
"lastInputTime": 0,
"sources": [
{
"previousRect": {
"x": 917.25,
"y": 708.25,
"width": 706.5,
"height": 248.5,
"top": 708.25,
"right": 1623.75,
"bottom": 956.75,
"left": 917.25
},
"currentRect": {
"x": 693.25,
"y": 708.25,
"width": 1154.5,
"height": 472.5,
"top": 708.25,
"right": 1847.75,
"bottom": 1180.75,
"left": 693.25
}
}
]
}
Specifications
| Specification |
|---|
| Layout Instability API # dom-layoutshift-tojson |