What is the difference between decodeURIComponent and decodeURI?

To explain the difference between these two let me explain the difference between encodeURI and encodeURIComponent.

The main difference is that:

• The encodeURI function is intended for use on the full URI.
• The encodeURIComponent function is intended to be used on .. well .. URI components that is any part that lies between separators (; / ? : @ & = + $ , #).

So, in encodeURIComponent these separators are encoded also because they are regarded as text and not special characters.

Now back to the difference between the decode functions, each function decodes strings generated by its corresponding encode counterpart taking care of the semantics of the special characters and their handling.

encodeURIComponent/decodeURIComponent() is almost always the pair you want to use, for concatenating together and splitting apart text strings in URI parts.

encodeURI in less common, and misleadingly named: it should really be called fixBrokenURI. It takes something that's nearly a URI, but has invalid characters such as spaces in it, and turns it into a real URI. It has a valid use in fixing up invalid URIs from user input, and it can also be used to turn an IRI (URI with bare Unicode characters in) into a plain URI (using %-escaped UTF-8 to encode the non-ASCII).

Where encodeURI should really be named fixBrokenURI(), decodeURI() could equally be called potentiallyBreakMyPreviouslyWorkingURI(). I can think of no valid use for it anywhere; avoid.

js> s = "http://www.example.com/string with + and ? and & and spaces";
http://www.example.com/string with + and ? and & and spaces
js> encodeURI(s)
http://www.example.com/string%20with%20+%20and%20?%20and%20&%20and%20spaces
js> encodeURIComponent(s)
http%3A%2F%2Fwww.example.com%2Fstring%20with%20%2B%20and%20%3F%20and%20%26%20and%20spaces

Looks like encodeURI produces a "safe" URI by encoding spaces and some other (e.g. nonprintable) characters, whereas encodeURIComponent additionally encodes the colon and slash and plus characters, and is meant to be used in query strings. The encoding of + and ? and & is of particular importance here, as these are special chars in query strings.

encodeURIComponent()

Converts the input into a URL-encoded string

encodeURI()

URL-encodes the input, but assumes a full URL is given, so returns a valid URL by not encoding the protocol (e.g. http://) and host name (e.g. www.stackoverflow.com).

decodeURIComponent() and decodeURI() are the opposite of the above

decodeURIComponent will decode URI special markers such as &, ?, #, etc, decodeURI will not.

encodeURIComponent Not Escaped:

A-Z a-z 0-9 - _ . ! ~ * ' ( )

encodeURI() Not Escaped:

A-Z a-z 0-9 ; , / ? : @ & = + $ - _ . ! ~ * ' ( ) #

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/encodeURIComponent

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/encodeURI

The encodeURI() function does not encode characters that have special meaning (reserved characters) for a URI.