Difference between decodeURIComponent() and decodeURI() functions in JavaScript

Both decodeURI() and decodeURIComponent() are Javascript global functions that are used for decoding encoded URI (Uniform Resource Identifier). 

JavaScript decodeURI() function: It decodes a string previously encoded by the encodeURI() function. It returns a decoded URI by replacing each UTF-8 escape sequence with the characters it represents.

Syntax:

decodeURI(encodeURI(x));

Parameters: It contains a single parameter that includes a string previously encoded by the encodeURI() function and hence result will be x again.

Example: This example uses decodeURI() function. 

HTML

<script type="text/javascript">
    var decodeText1 = decodeURI('http://www.testing.com/');
    console.log(decodeText1);
    var decodeText2 = decodeURI('http%3A%2F%2Fwww.testing.com%2F');
    console.log(decodeText2);
</script>

Output: 

http://www.testing.com/
http%3A%2F%2Fwww.testing.com%2F

JavaScript decodeURIComponent() function: It decodes a string previously encoded by the encodeURIComponent() function. It returns a decoded URI Component by replacing each UTF-8 escape sequence with the characters it represents. It can decode any value between %00 and %7F. 

Syntax:

decodeURIComponent(encodeURIComponent(x));

Parameters: Single parameter that includes a string previously encoded by encodeURIComponent() and hence result will be x again.

Example: This example is on decodeURIComponent() 

HTML

<script type="text/javascript">
    var decodeText1 = decodeURIComponent(
                    'http://www.testing.com/');
    console.log(decodeText1);

    var decodeText2 = decodeURIComponent(
            'http%3A%2F%2Fwww.testing.com%2F');
    console.log(decodeText2);
</script>

Output:

http://www.testing.com/
http://www.testing.com/

Note:Both functions throw URIError indicating that one or more of the escape sequences in string is malformed and cannot be correctly decoded.
Difference between decodeURIComponent() and decodeURI() Function:

• decodeURI(): It takes encodeURI(url) string so it cannot decoded characters (, / ? : @ & = + $ #)
• decodeURIComponent(): It takes encodeURIComponent(url) string so it can decode these characters.
  
• decodeURI(): It takes encodeURI(url) string as parameter and returns the decoded string.
• decodeURIComponent(): It takes encodeURIComponent(url) string as parameter and returns the decoded string.
• decodeURI(“%41”): It returns “A”
• decodeURIComponent(“%41”) It returns “A”
• decodeURI(“%26”): It returns “%26”
• decodeURIComponent(“%26”): It returns “&”