Get URL Parameters with JavaScript

Get URL Parameters with JavaScript

Get URL Parameters with JavaScript. In this JavaScript tutorial, we’ll show you how to parse and manipulate URL parameters using JavaScript. URL parameters (also called query string parameters or URL variables) are used to send small amounts of data from page to page, or from client to server via a URL. They can contain all kinds of useful information, such as search queries, link referrals, product information, user preferences, and more.

URL parameters (also called query string parameters or URL variables) are used to send small amounts of data from page to page, or from client to server via a URL. They can contain all kinds of useful information, such as search queries, link referrals, product information, user preferences, and more.

In this article, we’ll show you how to parse and manipulate URL parameters using JavaScript.

This article was updated in 2020 for relevance and accuracy.

Getting a URL Parameter

In modern browsers, this has become a lot easier, thanks to the URLSearchParams interface. This defines a host of utility methods to work with the query string of a URL.

Assuming that our URL is, we can grab the query string using

const queryString =;
// ?product=shirt&color=blue&newuser&size=m

We can then parse the query string’s parameters using URLSearchParams:

const urlParams = new URLSearchParams(queryString);

Then we call any of its methods on the result.

For example, URLSearchParams.get() will return the first value associated with the given search parameter:

const product = urlParams.get('product')
// shirt

const color = urlParams.get('color')
// blue

const newUser = urlParams.get('newuser')
// empty string

Other Useful Methods

Checking for the Presence of a Parameter

You can use URLSearchParams.has() to check whether a certain parameter exists:

// true

// false

Getting All of a Parameter’s Values

You can use URLSearchParams.getAll() to return all of the values associated with a particular parameter:

// [ 'm' ]

//Programmatically add a second size parameter.
urlParams.append('size', 'xl');

// [ 'm', 'xl' ]

Iterating over Parameters

URLSearchParams also provides some familiar Object iterator methods, allowing you iterate over its keys, values and entries:

  keys = urlParams.keys(),
  values = urlParams.values(),
  entries = urlParams.entries();

for (const key of keys) console.log(key);
// product, color, newuser, size

for (const value of values) console.log(value);
// shirt, blue, , m

for(const entry of entries) {
  console.log(`${entry[0]}: ${entry[1]}`);
// product: shirt
// color: blue
// newuser:
// size: m

Browser Support

Browser support for URLSearchParams is good. At the time of writing, it’s supported in all major browsers.

There’s a polyfill available if you have to support legacy browsers such as Internet Explorer. Or, you could follow along with the rest of this tutorial and learn how to roll your own.

Rolling Your Own Query String Parsing Function

Let’s stay with the URL we were using in the previous section:

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] :;

  // 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('=');

      // set parameter name and value (use 'true' if empty)
      var paramName = a[0];
      var paramValue = typeof (a[1]) === 'undefined' ? true : a[1];

      // (optional) keep case consistent
      paramName = paramName.toLowerCase();
      if (typeof paramValue === 'string') paramValue = paramValue.toLowerCase();

      // if the paramName ends with square brackets, e.g. colors[] or colors[2]
      if (paramName.match(/\[(\d+)?\]$/)) {

        // create key if it doesn't exist
        var key = paramName.replace(/\[(\d+)?\]/, '');
        if (!obj[key]) obj[key] = [];

        // if it's an indexed array e.g. colors[2]
        if (paramName.match(/\[\d+\]$/)) {
          // get the index value and add the entry at the appropriate position
          var index = /\[(\d+)\]/.exec(paramName)[1];
          obj[key][index] = paramValue;
        } else {
          // otherwise add the value to the end of the array
      } else {
        // we're dealing with a string
        if (!obj[paramName]) {
          // if it doesn't exist, create property
          obj[paramName] = paramValue;
        } else if (obj[paramName] && typeof obj[paramName] === 'string'){
          // if property does exist and it's a string, convert it to an array
          obj[paramName] = [obj[paramName]];
        } else {
          // otherwise add the property

  return obj;

You’ll see how this works soon, but first, here are some usage examples:

getAllUrlParams().product; // 'shirt'
getAllUrlParams().color; // 'blue'
getAllUrlParams().newuser; // true
getAllUrlParams().nonexistent; // undefined
getAllUrlParams('').a; // 'abc'

And here’s a demo for you to play around with.

Things to Know Before Using This Function
  • Our function assumes the parameters are separated by the & character, as indicated in the W3C specifications. However, the URL parameter format in general is not clearly defined, so you occasionally might see ; or &amp; as separators.

  • Our function still works if a parameter doesn’t have an equals sign or if it has an equals sign but no value.

  • The values of duplicate parameters get put into an array.

If you just wanted a function you could drop into your code, you’re done now. If you’d like to understand how the function works, read on.

The following section assumes you know some JavaScript, including functions, objects, and arrays. If you need a refresher, check out the MDN JavaScript reference.

How the Function Works

Overall, the function takes a URL’s query string (the part after the ? and before the #) and spits out the data in a neat object.

First, this line says, if we’ve specified a URL, get everything after the question mark, but otherwise, just use the URL of the window:

var queryString = url ? url.split('?')[1] :;

Next, we’ll create an object to store our parameters:

var obj = {};

If the query string exists, we’ll start parsing it. First we have to make sure to shave off the part starting from the #, since it’s not part of the query string:

queryString = queryString.split('#')[0];

Now we can split the query string into its component parts:

var arr = queryString.split('&');

That will give us an array that looks like this:

['product=shirt', 'color=blue', 'newuser', 'size=m']

Next, we’ll loop through this array and split each item into a key and a value, which we’ll soon put into our object:

var a = arr[i].split('=');

Let’s assign the key and a value to individual variables. If there isn’t a parameter value, we’ll set it to true to indicate that the parameter name exists. Feel free to change this depending on your use case:

var paramName = a[0];
var paramValue = typeof (a[1]) === 'undefined' ? true : a[1];

Optionally, you can set all parameter names and values to lowercase. That way, you can avoid situations where someone sends traffic to a URL with example=TRUE instead of example=true and your script breaks. (I’ve seen this happen.) However, if your query string needs to be case sensitive, feel free to omit this part:

paramName = paramName.toLowerCase();
if (typeof paramValue === 'string') paramValue = paramValue.toLowerCase();

Next, we need to deal with the various types of input we can receive in paramName. This could be an indexed array, a non-indexed array, or a regular string.

If it’s an indexed array, we want the corresponding paramValue to be an array, with the value inserted at the correct position. If it’s a non-indexed array, we want the corresponding paramValue to be an array with the element pushed on to it. If it’s a string, we want to create a regular property on the object and assign the paramValue to it, unless the property already exists, in which case we want to convert the existing paramValue to an array and push the incoming paramValue on to that.

To illustrate this, here’s some sample input, with the output we would expect:

// { "colors": [ "red", null, "green", null, null, null, "blue" ] }

// { "colors": [ "red", "green", "blue" ] }

// { "colors": [ "red", "green", "blue" ] }

// { "product": "shirt", "color": "blue", "newuser": true, "size": "m" }

And here’s the code to implement the functionality:

if (paramName.match(/\[(\d+)?\]$/)) {
  var key = paramName.replace(/\[(\d+)?\]/, '');
  if (!obj[key]) obj[key] = [];

  if (paramName.match(/\[\d+\]$/)) {
    var index = /\[(\d+)\]/.exec(paramName)[1];
    obj[key][index] = paramValue;
  } else {
} else {
  if (!obj[paramName]) {
    obj[paramName] = paramValue;
  } else if (obj[paramName] && typeof obj[paramName] === 'string'){
    obj[paramName] = [obj[paramName]];
  } else {

Finally, we return our object with the parameters and values.

If your URL has any encoded special characters like spaces (encoded as %20), you can also decode them to get the original value like this:

// assume a url parameter of test=a%20space

var original = getAllUrlParams().test; // 'a%20space'
var decoded = decodeURIComponent(original); // 'a space'

Just be careful not to decode something that’s already decoded or else your script will error out, especially if percents are involved.

Anyways, congrats! Now you know how to get a URL parameter, and hopefully have picked up some other tricks along the way.


The code in this article works for the most common use cases where you would get a URL query parameter. If you’re working with any edge cases, such as uncommon separators or special formatting, then be sure to test and adjust accordingly.

If you want to do more with URLs, there are specific libraries available, such as query-string and Medialize URI.js. But since it’s basically string manipulation, it often makes sense just to use plain JavaScript. Whether you use your own code or go with a library, be sure to check everything and make sure it works for your use cases.

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JavaScript developers should you be using Web Workers?

JavaScript developers should you be using Web Workers?

Do you think JavaScript developers should be making more use of Web Workers to shift execution off of the main thread?

Originally published by David Gilbertson at

So, Web Workers. Those wonderful little critters that allow us to execute JavaScript off the main thread.

Also known as “no, you’re thinking of Service Workers”.

Photo by Caleb Jones on Unsplash

Before I get into the meat of the article, please sit for a lesson in how computers work:

Understood? Good.

For the red/green colourblind, let me explain. While a CPU is doing one thing, it can’t be doing another thing, which means you can’t sort a big array while a user scrolls the screen.

This is bad, if you have a big array and users with fingers.

Enter, Web Workers. These split open the atomic concept of a ‘CPU’ and allow us to think in terms of threads. We can use one thread to handle user-facing work like touch events and rendering the UI, and different threads to carry out all other work.

Check that out, the main thread is green the whole way through, ready to receive and respond to the gentle caress of a user.

You’re excited (I can tell), if we only have UI code on the main thread and all other code can go in a worker, things are going to be amazing (said the way Oprah would say it).

But cool your jets for just a moment, because websites are mostly about the UI — it’s why we have screens. And a lot of a user’s interactions with your site will be tapping on the screen, waiting for a response, reading, tapping, looking, reading, and so on.

So we can’t just say “here’s some JS that takes 20ms to run, chuck it on a thread”, we must think about where that execution time exists in the user’s world of tap, read, look, read, tap…

I like to boil this down to one specific question:

Is the user waiting anyway?

Imagine we have created some sort of git-repository-hosting website that shows all sorts of things about a repository. We have a cool feature called ‘issues’. A user can even click an ‘issues’ tab in our website to see a list of all issues relating to the repository. Groundbreaking!

When our users click this issues tab, the site is going to fetch the issue data, process it in some way — perhaps sort, or format dates, or work out which icon to show — then render the UI.

Inside the user’s computer, that’ll look exactly like this.

Look at that processing stage, locking up the main thread even though it has nothing to do with the UI! That’s terrible, in theory.

But think about what the human is actually doing at this point. They’re waiting for the common trio of network/process/render; just sittin’ around with less to do than the Bolivian Navy.

Because we care about our users, we show a loading indicator to let them know we’ve received their request and are working on it — putting the human in a ‘waiting’ state. Let’s add that to the diagram.

Now that we have a human in the picture, we can mix in a Web Worker and think about the impact it will have on their life:


First thing to note is that we’re not doing anything in parallel. We need the data from the network before we process it, and we need to process the data before we can render the UI. The elapsed time doesn’t change.

(BTW, the time involved in moving data to a Web Worker and back is negligible: 1ms per 100 KB is a decent rule of thumb.)

So we can move work off the main thread and have a page that is responsive during that time, but to what end? If our user is sitting there looking at a spinner for 600ms, have we enriched their experience by having a responsive screen for the middle third?


I’ve fudged these diagrams a little bit to make them the gorgeous specimens of graphic design that they are, but they’re not really to scale.

When responding to a user request, you’ll find that the network and DOM-manipulating part of any given task take much, much longer than the pure-JS data processing part.

I saw an article recently making the case that updating a Redux store was a good candidate for Web Workers because it’s not UI work (and non-UI work doesn’t belong on the main thread).

Chucking the data processing over to a worker thread sounds sensible, but the idea struck me as a little, umm, academic.

First, let’s split instances of ‘updating a store’ into two categories:

  1. Updating a store in response to a user interaction, then updating the UI in response to the data change
  2. Not that first one

If the first scenario, a user taps a button on the screen — perhaps to change the sort order of a list. The store updates, and this results in a re-rendering of the DOM (since that’s the point of a store).

Let me just delete one thing from the previous diagram:

In my experience, it is rare that the store-updating step goes beyond a few dozen milliseconds, and is generally followed by ten times that in DOM updating, layout, and paint. If I’ve got a site that’s taking longer than this, I’d be asking questions about why I have so much data in the browser and so much DOM, rather than on which thread I should do my processing.

So the question we’re faced with is the same one from above: the user tapped something on the screen, we’re going to work on that request for hopefully less than a second, why would we want to make the screen responsive during that time?

OK what about the second scenario, where a store update isn’t in response to a user interaction? Performing an auto-save, for example — there’s nothing more annoying than an app becoming unresponsive doing something you didn’t ask it to do.

Actually there’s heaps of things more annoying than that. Teens, for example.

Anyhoo, if you’re doing an auto-save and taking 100ms to process data client-side before sending it off to a server, then you should absolutely use a Web Worker.

In fact, any ‘background’ task that the user hasn’t asked for, or isn’t waiting for, is a good candidate for moving to a Web Worker.

The matter of value

Complexity is expensive, and implementing Web Workers ain’t cheap.

If you’re using a bundler — and you are — you’ll have a lot of reading to do, and probably npm packages to install. If you’ve got a create-react-app app, prepare to eject (and put aside two days twice a year to update 30 different packages when the next version of Babel/Redux/React/ESLint comes out).

Also, if you want to share anything fancier than plain data between a worker and the main thread you’ve got some more reading to do (comlink is your friend).

What I’m getting at is this: if the benefit is real, but minimal, then you’ve gotta ask if there’s something else you could spend a day or two on with a greater benefit to your users.

This thinking is true of everything, of course, but I’ve found that Web Workers have a particularly poor benefit-to-effort ratio.

Hey David, why you hate Web Workers so bad?

Good question.

This is a doweling jig:

I own a doweling jig. I love my doweling jig. If I need to drill a hole into the end of a piece of wood and ensure that it’s perfectly perpendicular to the surface, I use my doweling jig.

But I don’t use it to eat breakfast. For that I use a spoon.

Four years ago I was working on some fancy animations. They looked slick on a fast device, but janky on a slow one. So I wrote fireball-js, which executes a rudimentary performance benchmark on the user’s device and returns a score, allowing me to run my animations only on devices that would render them smoothly.

Where’s the best spot to run some CPU intensive code that the user didn’t request? On a different thread, of course. A Web Worker was the correct tool for the job.

Fast forward to 2019 and you’ll find me writing a routing algorithm for a mapping application. This requires parsing a big fat GeoJSON map into a collection of nodes and edges, to be used when a user asks for directions. The processing isn’t in response to a user request and the user isn’t waiting on it. And so, a Web Worker is the correct tool for the job.

It was only when doing this that it dawned on me: in the intervening quartet of years, I have seen exactly zero other instances where Web Workers would have improved the user experience.

Contrast this with a recent resurgence in Web Worker wonderment, and combine that contrast with the fact that I couldn’t think of anything else to write about, then concatenate that combined contrast with my contrarian character and you’ve got yourself a blog post telling you that maybe Web Workers are a teeny-tiny bit overhyped.

Thanks for reading

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Further reading

An Introduction to Web Workers

JavaScript Web Workers: A Beginner’s Guide

Using Web Workers to Real-time Processing

How to use Web Workers in Angular app

Using Web Workers with Angular CLI

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