Return to Answer

Array
    .from(url.searchParams)
    .reduce((accum, [key, val]) => {
        accum[key] = val;
        return accum;
    }, {});
// -> { startIndex: '1', pageSize: '10' }

function searchParamsToObj(searchParams) {
  const paramsMap = Array
    .from(url.searchParams)
    .reduce((params, [key, val]) => params.set(key, val), new Map());
  return Object.fromEntries(paramsMap);
}
searchParamsToObj(url.searchParams);
// -> { startIndex: '1', pageSize: '10' }

url.searchParams.get('searchIndex');  // '1'

url.searchParams.get('startIndex');  // '1'

Array.from(url.searchParams).reduce((accum, [key, val]) => {
  accum[key] = val;
  return accum;
}, {});
// -> { startIndex: '1', pageSize: '10' }

// Simple object output (note: does NOT preserve duplicate keys).
var params = url.search.substr(1); // remove '?' prefix
params.split('&').reduce((accum, keyval) => {
  const [key, val] = keyval.split('=');
  accum[key] = val;
  return accum;
}, {});
// -> { startIndex: '1', pageSize: '10' }

Array
    .from(url.searchParams)
    .reduce((accum, [key, val]) => {
        accum[key] = val;
        return accum;
    }, {});
// -> { startIndex: '1', pageSize: '10' }

// Simple object output (note: does NOT preserve duplicate keys).
var params = url.search.substr(1); // remove '?' prefix
params
    .split('&')
    .reduce((accum, keyval) => {
        const [key, val] = keyval.split('=');
        accum[key] = val;
        return accum;
    }, {});
// -> { startIndex: '1', pageSize: '10' }