Cadena de consulta convertida a clave: formato de valor

/ ** 
 * @desc convierte la cadena de consulta en clave: valor 
 * @param {cadena} cadena de consulta-consulta '? a = chenfeng & b = ami & c = & d = 999'; 
 * @returns {object} 
 * / 
function getQueryMap (query) { 
  var queryMap = {}; 
  query.substr (1) // truncar '?' 
       .split ('&') // convertir a ['a = chenfeng', 'b = ami'] 
       .forEach (item => { 
         const [key, value] = item.split ('='); // ['a', 'chenfeng'] 
         queryMap [key] = value; 
       }); 

  return queryMap; 
} 

// {a : 'chenfeng', b: 'ami', c: '', d: '999'} 
console.log (getQueryMap ('? a = chenfeng & b = ami & c = & d = 999'));