Check out the built-in function encodeURIComponent(str) and encodeURI(str).
In your case, this should work:

var myOtherUrl = 
       "http://example.com/index.html?url=" + encodeURIComponent(myUrl);

You have three options:

• escape() will not encode: @*/+

• encodeURI() will not encode: ~!@#$&*()=:/,;?+'

• encodeURIComponent() will not encode: ~!*()'

But in your case, if you want to pass a URL into a GET parameter of other page, you should use escape or encodeURIComponent, but not encodeURI.

See Stack Overflow question Best practice: escape, or encodeURI / encodeURIComponent for further discussion.

Stick with encodeURIComponent(). The function encodeURI() does not bother to encode many characters that have semantic importance in URLs (e.g. "#", "?", and "&"). escape() is deprecated, and does not bother to encode "+" characters, which will be interpreted as encoded spaces on the server (and, as pointed out by others here, does not properly URL-encode non-ASCII characters).

There is a nice explanation of the difference between encodeURI() and encodeURIComponent() elsewhere. If you want to encode something so that it can safely be included as a component of a URI (e.g. as a query string parameter), you want to use encodeURIComponent().

The best answer is to use encodeURIComponent on values in the query string (and nowhere else).

However, I find that many older APIs want to replace " " with "+" so I've had to use the following:

const value = encodeURIComponent(value).replace('%20','+');
const url = 'http://example.com?lang=en&key=' + value

escape is implemented differently in different browsers and encodeURI doesn't encode many characters (like # and even /) -- it's made to be used on a full URI/URL without breaking it – which isn't super helpful or secure.

And as @Jochem points out below, you may want to use encodeURIComponent() on a (each) folder name, but for whatever reason these APIs don't seem to want + in folder names so plain old encodeURIComponent works great.

Example:

const escapedValue = encodeURIComponent(value).replace('%20','+');
const escapedFolder = encodeURIComponent('My Folder'); // no replace
const url = `http://example.com/${escapedFolder}/?myKey=${escapedValue}`;

I would suggest to use the qs npm package:

qs.stringify({a:"1=2", b:"Test 1"}); // gets a=1%3D2&b=Test+1

It is easier to use with a JavaScript object and it gives you the proper URL encoding for all parameters.

If you are using jQuery, I would go for the $.param method. It URL encodes an object, mapping fields to values, which is easier to read than calling an escape method on each value.

$.param({a:"1=2", b:"Test 1"}) // Gets a=1%3D2&b=Test+1

Modern solution (2021)

Since the other answers were written, the URLSearchParams API has been introduced. It can be used like this:

const queryParams = { param1: 'value1', param2: 'value2' }
const queryString = new URLSearchParams(queryParams).toString()
// 'param1=value1&param2=value2'

It also encodes non-URL characters.

For your specific example, you would use it like this:

const myUrl = "http://example.com/index.html?param=1&anotherParam=2";
const myOtherUrl = new URL("http://example.com/index.html");
myOtherUrl.search = new URLSearchParams({url: myUrl});
console.log(myOtherUrl.toString());

This solution is also mentioned here and here.

encodeURIComponent() is the way to go.

var myOtherUrl = "http://example.com/index.html?url=" + encodeURIComponent(myUrl);

But you should keep in mind that there are small differences from PHP version urlencode() and as @CMS mentioned, it will not encode every character. Guys at http://phpjs.org/functions/urlencode/ made JavaScript equivalent to phpencode():

function urlencode(str) {
  str = (str + '').toString();

  // Tilde should be allowed unescaped in future versions of PHP (as reflected below), but if you want to reflect current
  // PHP behavior, you would need to add ".replace(/~/g, '%7E');" to the following.
  return encodeURIComponent(str)
    .replace('!', '%21')
    .replace('\'', '%27')
    .replace('(', '%28')
    .replace(')', '%29')
    .replace('*', '%2A')
    .replace('%20', '+');
}

I think now in 2022 to be really safe, you should always consider constructing your URLs using the URL() interface. It'll do most of the job for you. So coming to your code,

const baseURL = 'http://example.com/index.html';

const myUrl = new URL(baseURL);
myUrl.searchParams.append('param', '1');
myUrl.searchParams.append('anotherParam', '2');

const myOtherUrl = new URL(baseURL);
myOtherUrl.searchParams.append('url', myUrl.href);

console.log(myUrl.href);
// Outputs: http://example.com/index.html?param=1&anotherParam=2
console.log(myOtherUrl.href);
// Outputs: http://example.com/index.html?url=http%3A%2F%2Fexample.com%2Findex.html%3Fparam%3D1%26anotherParam%3D2
console.log(myOtherUrl.searchParams.get('url'));
// Outputs: http://example.com/index.html?param=1&anotherParam=2

Or...

const params = new URLSearchParams(myOtherUrl.search);

console.log(params.get('url'));
// Outputs: http://example.com/index.html?param=1&anotherParam=2

Something like this is assured not to fail.

To encode a URL, as has been said before, you have two functions:

encodeURI()

and

encodeURIComponent()

The reason both exist is that the first preserves the URL with the risk of leaving too many things unescaped, while the second encodes everything needed.

With the first, you could copy the newly escaped URL into address bar (for example) and it would work. However your unescaped '&'s would interfere with field delimiters, the '='s would interfere with field names and values, and the '+'s would look like spaces. But for simple data when you want to preserve the URL nature of what you are escaping, this works.

The second is everything you need to do to make sure nothing in your string interfers with a URL. It leaves various unimportant characters unescaped so that the URL remains as human readable as possible without interference. A URL encoded this way will no longer work as a URL without unescaping it.

So if you can take the time, you always want to use encodeURIComponent() -- before adding on name/value pairs encode both the name and the value using this function before adding it to the query string.

I'm having a tough time coming up with reasons to use the encodeURI() -- I'll leave that to the smarter people.

What is URL encoding:

A URL should be encoded when there are special characters located inside the URL. For example:

console.log(encodeURIComponent('?notEncoded=&+'));

We can observe in this example that all characters except the string notEncoded are encoded with % signs. URL encoding is also known as percentage encoding because it escapes all special characters with a %. Then after this % sign every special character has a unique code

Why do we need URL encoding:

Certain characters have a special value in a URL string. For example, the ? character denotes the beginning of a query string. In order to successfully locate a resource on the web, it is necessary to distinguish between when a character is meant as a part of string or part of the URL structure.

How can we achieve URL encoding in JavaScript:

JavaScript offers a bunch of built-in utility functions which we can use to easily encode URLs. These are two convenient options:

1. encodeURIComponent(): Takes a component of a URI as an argument and returns the encoded URI string.
2. encodeURI(): Takes a URI as an argument and returns the encoded URI string.

Example and caveats:

Be aware of not passing in the whole URL (including scheme, e.g., https://) into encodeURIComponent(). This can actually transform it into a not functional URL. For example:

// for a whole URI don't use encodeURIComponent it will transform
// the / characters and the URL won't fucntion properly
console.log(encodeURIComponent("http://www.random.com/specials&char.html"));

// instead use encodeURI for whole URL's
console.log(encodeURI("http://www.random.com/specials&char.html"));

We can observe f we put the whole URL in encodeURIComponent that the forward slashes (/) are also converted to special characters. This will cause the URL to not function properly anymore.

Therefore (as the name implies) use:

1. encodeURIComponent on a certain part of a URL which you want to encode.
2. encodeURI on a whole URL which you want to encode.

To prevent double encoding, it's a good idea to decode the URL before encoding (if you are dealing with user entered URLs for example, which might be already encoded).

Let’s say we have abc%20xyz 123 as input (one space is already encoded):

encodeURI("abc%20xyz 123")            //   Wrong: "abc%2520xyz%20123"
encodeURI(decodeURI("abc%20xyz 123")) // Correct: "abc%20xyz%20123"

You should not use encodeURIComponent() directly.

Take a look at RFC3986: Uniform Resource Identifier (URI): Generic Syntax

sub-delims = "!" / "$" / "&" / "'" / "(" / ")" / "*" / "+" / "," / ";" / "="

The purpose of reserved characters is to provide a set of delimiting characters that are distinguishable from other data within a URI.

These reserved characters from the URI definition in RFC3986 ARE NOT escaped by encodeURIComponent().

MDN Web Docs: encodeURIComponent()

To be more stringent in adhering to RFC 3986 (which reserves !, ', (, ), and *), even though these characters have no formalized URI delimiting uses, the following can be safely used:

Use the MDN Web Docs function...

function fixedEncodeURIComponent(str) {
  return encodeURIComponent(str).replace(/[!'()*]/g, function(c) {
    return '%' + c.charCodeAt(0).toString(16);
  });
}

A similar kind of thing I tried with normal JavaScript:

function fixedEncodeURIComponent(str){
    return encodeURIComponent(str).replace(/[!'()]/g, escape).replace(/\*/g, "%2A");
}

Performance

Today (2020.06.12) I performed a speed test for chosen solutions on macOS v10.13.6 (High Sierra) on browsers Chrome 83.0, Safari 13.1, and Firefox 77.0. This results can be useful for massive URLs encoding.

Conclusions

• encodeURI (B) seems to be fastest, but it is not recommended for URLs
• escape (A) is a fast cross-browser solution
• solution F recommended by MDN is medium fast
• solution D is slowest

Details

For solutions A B C D E F I perform two tests

• for short URL - 50 characters - you can run it HERE
• for long URL - 1M characters - you can run it HERE

function A(url) {
    return escape(url);
}

function B(url) {
    return encodeURI(url);
}

function C(url) {
    return encodeURIComponent(url);
}

function D(url) {
    return new URLSearchParams({url}).toString();
}

function E(url){
     return encodeURIComponent(url).replace(/[!'()]/g, escape).replace(/\*/g, "%2A");
}

function F(url) {
  return encodeURIComponent(url).replace(/[!'()*]/g, function(c) {
    return '%' + c.charCodeAt(0).toString(16);
  });
}



// ----------
// TEST
// ----------

var myUrl = "http://example.com/index.html?param=1&anotherParam=2";

[A,B,C,D,E,F]
  .forEach(f=> console.log(`${f.name} ?url=${f(myUrl).replace(/^url=/,'')}`));

This snippet only presents code of chosen solutions

Example results for Chrome

Nothing worked for me. All I was seeing was the HTML of the login page, coming back to the client side with code 200. (302 at first but the same Ajax request loading login page inside another Ajax request, which was supposed to be a redirect rather than loading plain text of the login page).

In the login controller, I added this line:

Response.Headers["land"] = "login";

And in the global Ajax handler, I did this:

$(function () {
    var $document = $(document);
    $document.ajaxSuccess(function (e, response, request) {
        var land = response.getResponseHeader('land');
        var redrUrl = '/login?ReturnUrl=' + encodeURIComponent(window.location);
        if(land) {
            if (land.toString() === 'login') {
                window.location = redrUrl;
            }
        }
    });
});

Now I don't have any issue, and it works like a charm.

Use fixedEncodeURIComponent function to strictly comply with RFC 3986:

function fixedEncodeURIComponent(str) {
  return encodeURIComponent(str).replace(/[!'()*]/g, function(c) {
    return '%' + c.charCodeAt(0).toString(16);
  });
}

Here is a live demo of encodeURIComponent() and decodeURIComponent() JavaScript built-in functions:

<!DOCTYPE html>
<html>
  <head>
    <style>
      textarea{
        width: 30%;
        height: 100px;
      }
    </style>
    <script>
      // Encode string to Base64
      function encode()
      {
        var txt = document.getElementById("txt1").value;
        var result = btoa(txt);
        document.getElementById("txt2").value = result;
      }
      // Decode Base64 back to original string
      function decode()
      {
        var txt = document.getElementById("txt3").value;
        var result = atob(txt);
        document.getElementById("txt4").value = result;
      }
    </script>
  </head>
  <body>
    <div>
      <textarea id="txt1">Some text to decode
      </textarea>
    </div>
    <div>
      <input type="button" id="btnencode" value="Encode" onClick="encode()"/>
    </div>
    <div>
      <textarea id="txt2">
      </textarea>
    </div>
    <br/>
    <div>
      <textarea id="txt3">U29tZSB0ZXh0IHRvIGRlY29kZQ==
      </textarea>
    </div>
    <div>
      <input type="button" id="btndecode" value="Decode" onClick="decode()"/>
    </div>
    <div>
      <textarea id="txt4">
      </textarea>
    </div>
  </body>
</html>

Encode URL String

var url = $(location).attr('href'); // Get the current URL

// Or
var url = 'folder/index.html?param=#23dd&noob=yes'; // Or specify one

var encodedUrl = encodeURIComponent(url);
console.log(encodedUrl);
// Outputs folder%2Findex.html%3Fparam%3D%2323dd%26noob%3Dyes

For more information, go to, jQuery Encode/Decode URL String.

You can use ESAPI library and encode your URL using the below function. The function ensures that '/'s are not lost to encoding while the remainder of the text contents are encoded:

function encodeUrl(url)
{
    String arr[] = url.split("/");
    String encodedUrl = "";
    for(int i = 0; i<arr.length; i++)
    {
        encodedUrl = encodedUrl + ESAPI.encoder().encodeForHTML(ESAPI.encoder().encodeForURL(arr[i]));
        if(i<arr.length-1) encodedUrl = encodedUrl + "/";
    }
    return url;
}

Don't forget the /g flag to replace all encoded ' '

var myOtherUrl = "http://example.com/index.html?url=" + encodeURIComponent(myUrl).replace(/%20/g,'+');

I always use this to encode stuff for URLs. This is completely safe because it will encode every single character even if it doesn't have to be encoded.

function urlEncode(text) {
    let encoded = '';
    for (let char of text) {
        encoded += '%' + char.charCodeAt(0).toString(16);
    }
    return encoded;
}

let name = `bbb`;
params = `name=${name}`;
var myOtherUrl = `http://example.com/index.html?url=${encodeURIComponent(params)}`;
console.log(myOtherUrl); 

Use backtick now in ES6 to encode urls

try this - https://bbbootstrap.com/code/encode-url-javascript-26885283