Introduction to the URL Object in JavaScript

Manipulating and extracting parts from a URL is a pain if we have to write all the code ourselves. Fortunately, most browsers have the URL object built into their standard library. Now, we can pass in the URL, as a string, to the URL constructor and create an instance of it. Then, we can use the handy value properties and methods to manipulate and get the parts of a URL that we want.

To create a URL object with the URL constructor, we use the new keyword like in the following code:

new URL('http://medium.com');

In above code, we create an instance of the URL object with an absolute URL. We can also create a URL object by passing-in a relative URL as the first argument and the base URL as the second argument. For example, we can write:

new URL('/@hohanga', 'http://medium.com');

Note that the second argument must be a base URL. This means that it must be a valid URL and not just part of it. It must start with the protocol like http:// or https://. We can also define them in a chain-like in the following code:

const mozillaUrl = 'https://developer.mozilla.org';
const mozillaDevUrl = new URL("/", mozillaUrl);
const mozillaUrl2 = new URL(mozillaUrl);
const docsUrl = new URL('/en-US/docs', mozillaUrl2);
const urlUrl = new URL('Web/API/URL', docsUrl);

If we call toString() on the URL objects above, we should get something like:

https://developer.mozilla.org
https://developer.mozilla.org/
https://developer.mozilla.org/
https://developer.mozilla.org/en-US/docs
https://developer.mozilla.org/en-US/Web/API/URL

The second argument is an optional argument and it should only be passed in when the first argument is a relative URL. The strings or URL objects that we pass in are converted to USVString objects which correspond to the set of all possible sequences of Unicode scalar values. In our code, we can treat them the same as regular strings. A TypeError will be thrown if both argument are relative URLs or if the base and the relative URL together aren’t valid. We can pass in the URL object directly to the second argument because the toString method of the URL object will convert a URL object into a full URL string before being manipulated in the constructor.

A URL object can have the following properties. This article will have the first half of the list of properties and Part 2 of this article will have the second half.

Hash Property

The hash property has the part of the URL that comes after the pound sign (# ). The string isn’t percent decoded, so special symbols like the following are still encoded. They’re encoding with the following mapping. The characters on the left side are converted to the ones on the right side during encoding:

  • ‘:’%3A
  • ‘/’%2F
  • ‘?’%3F
  • ‘#’%23
  • ‘[‘%5B
  • ‘]’%5D
  • ‘@’%40
  • ‘!’%21
  • ‘$’%24
  • “‘“%27
  • ‘(‘%28
  • ‘)’%29
  • ‘*’%2A
  • ‘+’%2B
  • ‘,’%2C
  • ‘;’%3B
  • ‘=’%3D
  • ‘%’%25
  • ‘ ‘%20 or +

For example, if we have the URL [https://example.com#hash](https://example.com#hash') . Then we can extract the hash with the hash property as follows:

const exampleUrl = new URL(‘https://example.com#hash');
console.log(exampleUrl.hash);

Then we get '#hash' in the console.log statement. The property is a USVString , but it’s converted to a string when we retrieve it like we did above. This is not a read-only property, so we can also assign to it like in the following code:

exampleUrl.hash = '#newHash';

For example, if we have:

const exampleUrl = new URL('https://example.com#hash');
exampleUrl.hash = '#newHash';
console.log(exampleUrl.hash);

Then we get [https://example.com/#newHash](https://example.com/#newHash) as the new URL when we get it with the href property.

Host Property

The host property of the URL object is a USVString that contains the host name. If a port is included after the : , then we also get the port number along with the host. For example, if we have:

const exampleUrl = new URL(‘https://example.com:8888');
console.log(exampleUrl.host);

Then we get example.com:8888 . Like other USVString properties, it’s converted to a string when we retrieve it. This is not a read only property, so we can also assign to it like in the following code:

exampleUrl.host = 'example.com';

We can also set the host property to change the URL structure. For example, if we have:

const exampleUrl = new URL('https://example.com:8888/en-US/docs/Web/API/URL/href/');

exampleUrl.host = 'newExample.com';
console.log(exampleUrl);

Then we get [https://newexample.com:8888/en-US/docs/Web/API/URL/href/](https://newexample.com:8888/en-US/docs/Web/API/URL/href/) as the new URL when we get it with the href property.

Hostname Property

With the hostname property, we can get the host name from the URL as a USVString. It will not include the port even if it’s included in the URL string that we used to construct the URL object. For example, if we have:

const exampleUrl = new URL(‘https://example.com:8888');
console.log(exampleUrl.hostname);

Then we get example.com from the console.log statement. Like other USVString properties, it’s converted to a string when we retrieve it. This is not a read-only property, so we can also assign to it like in the following code:

exampleUrl.hostname = ‘newExample.com’;

Then we get that the new URL is [https://newexample.com:8888/](https://newexample.com:8888/en-US/docs/Web/API/URL/href/) when we get it with the href property.

Href Property

The href property of the URL object is USVString that has the whole URL. For example, if we have:

const exampleUrl = new URL(‘https://example.com:8888/en-US/docs/Web/API/URL/href/');
console.log(exampleUrl.href);

Then when we run the code above, we get [https://example.com:8888/](https://example.com#hash')en-US/docs/Web/API/URL/href/ which is what we passed into the URL constructor. We can also set the href property by assigning our own value to it. For example, we can write:

const exampleUrl = new URL(‘https://example.com:8888/en-US/docs/Web/API/URL/href/');
exampleUrl.href = 'https://newExample.com';
console.log(exampleUrl.href);

Origin Property

The origin property is a read-only property that returns a USVString with the Unicode serialization of the origin of the URL. The structure of the origin will depend on the type of URL that’s used to construct the URL object. For http or https URLs, the origin will be the protocol followed by :// , then followed by the domain, then followed by the colon (: ), then followed by the port. The default port will only be omitted, which is 80 for http and 443 for https , if it’s explicitly specified. For file protocol URLs, the value will be browser dependent. For blob: URLs, the origin will be the part following blob: . For example, "blob:http://example.com" will be returned as "http://example.com" . For example, if we have:

const url = new URL("https://example.org:443")
console.log(url.origin);

Then we get:

https://example.org

If we have an http URL like the following:

const url = new URL("http://example.org:80")
console.log(url.origin);

Then we get:

http://example.org

If we have a non-default port for http or https URLs, like in the following:

const url = new URL("http://example.org:8888")
console.log(url.origin);

const url2 = new URL("http://example.org:8888")
console.log(url.origin);

Then we get [http://example.org:8888](http://example.org:8888)
and [http://example.org:8888](http://example.org:8888) respectively.

If we have a blob URL, like in the following:

const url = new URL("blob:http://example.org:8888")
console.log(url.origin);

Then we get [http://example.org:8888](http://example.org:8888) . And for file URLs like the following:

const url = new URL("file://c:/documents/document.docx")
console.log(url.origin);

Then we get file:// in Chrome.

Password Property

The password property is a writable property that extracts the password portion of the URL before the domain name. Like the other properties, the string is a USVString . If it’s set without the username property being set first, then assigning to this property will silently fail. For example, if we have:

const url = new URL('https://username:password@example.com');
console.log(url.password);

Then we get password in the console.log statement above. We can also set the password property to the password of our choice. For example, if we have:

const url = new URL('https://username:password@example.com');
url.password = 'newPassword'
console.log(url);

Then we get [https://username:newPassword@example.com](https://username:newPassword@example.com) as the new URL when we get it with the href property.

Pathname Property

The pathname property is a USVString property which has the part following the first slash (/). It’s writable property. For example, we can get the pathname value from the URL in the following code:

const url = new URL('https://example.com/path1/path2');
console.log(url.pathname);

Then we get /path1/path2 when we run the console.log statement above. We can also set the pathname property to the relative URL of your choice by setting it to the part after the domain. For example, we can write:

const url = new URL('https://example.com/path1/path2');
url.pathname = '/newpath1/newpath2';
console.log(url.href);

Then we get [https://example.com/newpath1/newpath2](https://example.com/newpath1/newpath2) when we run the console.log statement above.

Manipulating and extract parts from a URL is a pain if we have to write all the code to do it ourselves. Fortunately, most browsers have the URL object built in to their standard library. Now we can pass in the URL as a string to the URL constructor and to create an instance of a URL. Then we can use the handy value properties and methods to manipulate and get the parts of a URL that we want.

To create an URL object with the URL constructor, we use the new keyword like in the following code:

new URL('http://medium.com');

To see more ways to create an URL object, see Part 1 for more details.

A URL object can have the following properties. This article will have the second half of the list of properties and Part 1 of this article will have the first half. All string values are stored as USVString. USVString are objects which correspond to the set of all possible sequences of Unicode scalar values. All USVString values are converted to strings before we get them, so we can treat them all like regular strings.

Value Properties

port Property

The port property is a USVString property that has the port number of the URL. For example, if we have:

const url = new URL('https://example.com:8888');
console.log(url.port);

Then we get 8888 from the console.log statement. We can also set the port to get a new URL with by assigning the port property with a new value. For example, if we have the following code:

const url = new URL('https://example.com:8888');
url.port = '3333';
console.log(url.href);

Then we get [https://example.com:3333/](https://example.com:3333/) from the console.log statement when we run the code above.

protocol Property

With the protocol property, we can get the the protocol portion of the URL as a USVString , which is the very first part of the URL. Example protocols include http: , https: , ftp: , file: , etc. For instance, if we have the URL [https://example.com](https://example.com:8888'), then https is the protocol portion of the URL. If we have the following code:

const url = new URL('https://example.com:8888');
console.log(url.protocol);

Then we get https: from the console.log statement in the code above.

For other protocols like ftp , it also works:

const url = new URL('ftp://example.com:8888');
console.log(url.protocol);

If we run the code above, then we get ftp: from the console.log statement in the code above.

We can also set the protocol property to get a new URL. For example, if we have:

const url = new URL('ftp://example.com:8888');
url.protocol = 'http://'
console.log(url.href);

Then we get [http://example.com:8888/](http://example.com:8888/) from the console.log above. It also works if we omit the slashes or omit both the colon and the slashes. For example, if we have:

const url = new URL('ftp://example.com:8888');
url.protocol = 'http:'
console.log(url.href);

Then we also get [http://example.com:8888/](http://example.com:8888/) from the console.log above. Likewise, if we have:

const url = new URL('ftp://example.com:8888');
url.protocol = 'http'
console.log(url.href);

We get the same thing.

search Property

To get the search string or query string from a URL, we can use the search property. The query string is anything after the ? in a URL. Like all the other properties, this one is also USVString property. Note that this property get the whole query string. If you want the individual keys and values from the query string, then we can use the searchParams property. We can use the search property like the following code:

const url = new URL('http://example.com:8888?key1=value1&key2=value2');
console.log(url.search);

Then we get back ?key1=value1&key2=value2 from the console.log statement when we run the code above. We can also change the query string of the URL by assigning it a new value. For example, if we have the following code:

const url = new URL('http://example.com:8888?key1=value1&key2=value2');
url.search = 'newKey1=newValue1&newKey2=newValue2';
console.log(url.href);

Then we get [http://example.com:8888/?newKey1=newValue1&newKey2=newValue2](http://example.com:8888/?newKey1=newValue1&newKey2=newValue2) from the console.log statement when we run the code above.

searchParams Property

The search property only gets us the whole query string. To parse the query string into keys and values, we can use the searchParams property, which will get us a URLSearchParams object which has the list of keys and values listed on the query string. The keys and values will be decoded so that special characters are all intact. This is a read only property so we can’t set the query string directly by assigning a new value to this property. For example, to get the query string as a list of keys and values, we can write the following code:

const url = new URL('http://example.com:8888/?key1=value1&key2=value2');
console.log(url.searchParams.get('key1'));
console.log(url.searchParams.get('key2'));

Then we get value1 from the first console.log statement and value2 from the second console.log statement. The URLSearchParams object has a get method to get the value of the given query string key by the key name.

Username Property

We can get and set the username part of the URL with the username property. The username is a URL comes before the password and domain name. For example, if we have the following code:

const url = new URL('http://username:password@example.com');
console.log(url.username);

Then when we run the code above, we get username from the console.log statement above. Also, we can use it to set the username in a URL. For instance, if we have the following code:

const url = new URL('http://username:password@example.com');
url.username = 'newUserName';
console.log(url.href);

Then we get [http://newUserName:password@example.com/](http://newUserName:password@example.com/) from the console.log statement in the code above.

Instance Methods

URL object instances also have 2 methods. It has a toString() and a toJSON() method. The toString() method returns a USVString containing the whole URL. It’s the same as the href property for getting the whole URL, but we can’t use the toString() method to set the whole URL like we do with the href property. For example, if we have:

const url = new URL('http://username:password@example.com');
console.log(url.toString());

Then we get [http://username:password@example.com/](http://username:password@example.com/) from the console.log statement above.

The toJSON() method returns a JSON serialized version of the URL object. However, in most cases, it’s actually the same as what toString() will return. For example, if we have:

const url = new URL('http://username:password@example.com');
console.log(url.toJSON());
console.log(url.toString());
console.log(url.toJSON() === url.toString());

Then we get:

http://username:password@example.com/
http://username:password@example.com/
true

from the console.log statements when the code above is run. Then url.toJSON() and url.toString() calls returned the same output, and it’s confirmed by the comparison statement url.toJSON() === url.toString() , which evaluated to true .

Static Methods

There are 2 static methods in the URL constructor. It has the createObjectURL() method and the revokeObjectURL() method. The createObjectURL() static method creates a DOMString containing a URL representing the object given in the parameter. A DOMString is a UTF-16 encoded string. Since JavaScript uses UTF-16 strings, DOMStrings are mapped directly to strings. Passing null to a method that accepts a DOMString will convert null to 'null' . The createObbjectURL() method accepts an object, which can be a File, Blob, or MediaSource object to create a URL for.For example, we can call the createObjectURL() method like in the following code:

const objUrl = URL.createObjectURL(new File([""], "filename"));
console.log(objUrl);

Then we get something like:

blob:https://fiddle.jshell.net/4cfe2ef3-74ea-4145-87a7-0483b117b429

Each time we create an object URL with the createObjectURL() method, we have to release it by calling the revokeObjectURL() method to clear it from memory. However, browser will release object URLs automatically when the document is unloaded, but for the sake for improving performance, we should release it manually. The revokeObjectURL() method takes in an object URL as its argument. For example, if we have the object URL above created, then we can use the revokeObjectURL() method to release the object URL from memory like in the following code:

const objUrl = URL.createObjectURL(new File([""], "filename"));
console.log(objUrl);
URL.revokeObjectURL(objUrl);

The revokeObjectURL() method returns undefined .

When any part of the URL has special characters, they’re encoded by the rules found in RFC-3896, which has a long list of rules on how to encode different types of characters. It also includes non-English characters, and the percent encoding standard for encoding URLs. The full list of rules are at https://tools.ietf.org/html/rfc3986.

With the URL object, manipulating and extract parts from a URL is no longer a pain since we don’t have to write all the code to do it ourselves. Most browsers have the URL object built in to their standard library. Now we can pass in the URL as a string to the URL constructor and to create an instance of a URL. Then we can use the handy value properties and methods to manipulate and get the parts of a URL that we want. It can manipulate all parts of the URL except the query string portion, which can be manipulated by parsing it into a URLSeachParams object and then call its methods and set its properties to modify the query string. To toString and toJSON methods both convert a URL object into a full URL string.

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