URLSearchParams.getAll()

The getAll() method of the URLSearchParams interface returns all the values associated with a given search parameter as an array. 

URLSearchParams.getAll(name)

name

The name of the parameter to return.

An array of USVStrings.

let url = new URL('https://example.com?foo=1&bar=2');
let params = new URLSearchParams(url.search.slice(1));

//Add a second foo parameter.
params.append('foo', 4);

console.log(params.getAll('foo')) //Prints ["1","4"].