Tutorial :What is the difference between decodeURIComponent and decodeURI?


What is the difference between the JavaScript functions decodeURIComponent and decodeURI?


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

The main difference is that:

  • encodeURI is intended for use on the full URI.
  • encodeURIComponent 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).

decodeURI decodes the same characters as decodeURIComponent except for a few special ones. It is provided to be an inverse of encodeURI, but you still can't count on it to return the same as you originally put in â€" see eg. decodeURI(encodeURI('%20 '));.

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.



Converts the input into a URL-encoded string


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


As I had the same question, but didn't find the answer here, I made some tests in order to figure out what the difference actually is. I did this, since I need the encoding for something, which is not URL/URI related.

  • encodeURIComponent("A") returns "A", it does not encode "A" to "%41"
  • decodeURIComponent("%41") returns "A".
  • encodeURI("A") returns "A", it does not encode "A" to "%41"
  • decodeURI("%41") returns "A".

-That means both can decode alphanumeric characters, even though they did not encode them. However...

  • encodeURIComponent("&") returns "%26".
  • decodeURIComponent("%26") returns "&".
  • encodeURI("&") returns "&".
  • decodeURI("%26") returns "%26".

Even though encodeURIComponent does not encode all characters, decodeURIComponent can decode any value between %00 and %7F.

Note: It appears that if you try to decode a value above %7F (unless it's a unicode value), then your script will fail with an "URI error".


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

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