URLSearchParams.get()

The get() method of the URLSearchParams interface returns the first value associated to the given search parameter.

name

The name of the parameter to return.

A string if the given search parameter is found; otherwise, null.

If the URL of your page is https://example.com/?name=Jonathan&age=18 you could parse out the 'name' and 'age' parameters using:

let params = new URLSearchParams(document.location.search);
let name = params.get("name"); // is the string "Jonathan"
let age = parseInt(params.get("age"), 10); // is the number 18

Requesting a parameter that isn't present in the query string will return null:

let address = params.get("address"); // null