Setting form fields with query string

query-string-form-fill.js

function parseSearchString () {
  var qs = window.location.search
  qs = qs.replace(/^\?/,'')
  var parts = qs.split('&')
  var params = {}
  parts.forEach(function (part) {
    var pair = part.split('=')
    params[pair[0]] = decodeURIComponent(pair[1])
  })
  return params
}

window.onload = function () {
  var qs = parseSearchString()
  Object.keys(qs).forEach(function (key) {
    var elByName = document.querySelectorAll('[name=' + key + ']');
    var elByID = document.querySelectorAll('#' + key);
    // first try to set element value with provided name
    if (elByName.length) {
      elByName[0].value = qs[key];
    }
    // otherwise, try to set element value by id
    else if (elByID.length) {
     elByID[0].value = qs[key];
    }
    // .. more things
  });
}