Quick Tip: Get URL Parameters with JavaScript

So you want to get a parameter from a URL? URL parameters (also called query string parameters or URL variables) can have lots of useful data including product info, user preferences, link referrals, and more.

Let’s get started!

Getting URL Parameters

Let’s say you have the following url:

http://example.com/?product=shirt&color=blue&newuser&size=m

Here’s a function to give you all the URL parameters as a neat object:

function getAllUrlParams(url) {

  // get query string from url (optional) or window
  var queryString = url ? url.split('?')[1] : window.location.search.slice(1);

  // we'll store the parameters here
  var obj = {};

  // if query string exists
  if (queryString) {

    // stuff after # is not part of query string, so get rid of it
    queryString = queryString.split('#')[0];

    // split our query string into its component parts
    var arr = queryString.split('&');

    for (var i=0; i<arr.length; i++) {
      // separate the keys and the values
      var a = arr[i].split('=');

      // in case params look like: list[]=thing1&list[]=thing2
      var paramNum = undefined;
      var paramName = a[0].replace(/[d*]/, function(v) {
        paramNum = v.slice(1,-1);
        return '';
      });

      // set parameter value (use 'true' if empty)
      var paramValue = typeof(a[1])==='undefined' ? true : a[1];

      // (optional) keep case consistent
      paramName = paramName.toLowerCase();
      paramValue = paramValue.toLowerCase();

      // if parameter name already exists
      if (obj[paramName]) {
        // convert value to array (if still string)
        if (typeof obj[paramName] === 'string') {
          obj[paramName] = [obj[paramName]];
        }
        // if no array index number specified...
        if (typeof paramNum === 'undefined') {
          // put the value on the end of the array
          obj[paramName].push(paramValue);
        }
        // if array index number specified...
        else {
          // put the value at that index number
          obj[paramName][paramNum] = paramValue;
        }
      }
      // if param name doesn't exist yet, set it
      else {
        obj[paramName] = paramValue;
      }
    }
  }

  return obj;
}

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Source: Sitepoint