Recupera parâmetro de uma querystring

requestQueryString.js

const requestQuery = request => {
    const param = request.replace(/[\[]/, "\\[").replace(/[\]]/, "\\]")
    const regex = new RegExp("[\\?&]" + param + "=([^&#]*)")
    const results = regex.exec(location.search);
    return results == null ? "" : decodeURIComponent(results[1].replace(/\+/g, " "))

}

// caso de uso
// http://endereco.com.br?param1=123&param2=456&param3=789

console.log(requestQuery('param1')) // 123
console.log(requestQuery('param2')) // 456
console.log(requestQuery('param3')) // 789