encode_query_string.js

function encode_query_string(x) {
  let output = [];
  Object.keys(x).forEach(function(key) {
    output.push(`${encodeURIComponent(key)}=${encodeURIComponent(x[key])}`);
  });
  return output.join('&');
}

function decode_query_string(x) {
  let output = {};
  x.split('&').forEach(function(item) {
    let idx = item.indexOf('=');
    output[decodeURIComponent(item.slice(0, idx))] = decodeURIComponent(item.slice(idx + 1));
  });
  return output;
}

encode_query_string(decode_query_string(window.location.search.slice(1)))