With PHP

echo urlencode("http://www.image.com/?username=unknown&password=unknown");

Result

http%3A%2F%2Fwww.image.com%2F%3Fusername%3Dunknown%26password%3Dunknown

With Javascript:

var myUrl = "http://www.image.com/?username=unknown&password=unknown";
var encodedURL= "http://www.foobar.com/foo?imageurl=" + encodeURIComponent(myUrl);

DEMO: http://jsfiddle.net/Lpv53/

You can use one of these:

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

Example:

var url = new URL("http://foo.bar/?x=1&y=2");

// If your expected result is "http://foo.bar/?x=1&y=2&x=42"
url.searchParams.append('x', 42);

// If your expected result is "http://foo.bar/?x=42&y=2"
url.searchParams.set('x', 42);

You can use url.href or url.toString() to get the full URL

URLSearchParams has increasing browser support.

const data = {
  var1: 'value1',
  var2: 'value2'
};

const searchParams = new URLSearchParams(data);

// searchParams.toString() === 'var1=value1&var2=value2'

Node.js offers the querystring module.

const querystring = require('querystring');

const data = {
  var1: 'value1',
  var2: 'value2'
};

const searchParams = querystring.stringify(data);

// searchParams === 'var1=value1&var2=value2'

encodeURIComponent() should work. For example,

'&url=' + encodeURIComponent("http://a.com/?q=query&n=10")

produces

"&url=http%3A%2F%2Fa.com%2F%3Fq%3Dquery%26n%3D10"

(which doesn't have any & or ? in the value). When your server gets this url, it should be able to decode that to get the original:

param["url"] = "http://a.com/?q=query&n=10"

I'm not sure what server you're using (e.g. Rails, Django, ...) but that should work "out of the box" on any normal system.