The read-only URLSearchParams.size property indicates the total number of search parameter entries.

A number indicating the total number of search parameter entries in the URLSearchParams object.

You can get the total number of search parameter entries like so:

const searchParams = new URLSearchParams("c=4&a=2&b=3&a=1");
searchParams.size; // 4

Note how the a parameter is given twice, but size returns the number of all given entries (4) and not 3. To get the amount of unique keys, you can use a Set, for example:

[...new Set(searchParams.keys())].length; // 3

The size property is useful for checking whether there are any search parameters at all:

const url = new URL("https://example.com?foo=1&bar=2");

if (url.searchParams.size) {
  console.log("URL has search parameters!");
}

• URL.searchParams
• Polyfill of URLSearchParams in core-js