Regular Expression - can't checking for special characters [ ]

Question

I am trying to write a regular expression to check for the following characters: ( ) { } [ ]

The following code takes what the user has entered and console logs a message depending on whether they have entered an invalid character. The problem I am having is that I cannot get it to check for both [ ] characters - the code below checks for [ but not ]

 var nameString = $("#name").val();
    var  regexp =  /[(){}[]/;
    var invalidCharacters = nameString.match(regexp);
        if(invalidCharacters){
                console.log('Contains invalid character');
                } else{
               console.log('DOES NOT contain an invalid character');
           }

How do I add ] and keep the regex valid?

Answer 1

You must place the ] in the beginning, like so,

var  regexp =  /[](){}[]/;

Now, understandably, this looks weird. It looks like an empty character class, [], followed by pairs of brackets, (), {}, and []. But believe it or not, it's actually the standard in regular expressions to disregard the ] as indicating the end of a character class if it's the first character present. Therefore the above is actually a character class for the characters ](){}[.

You might also rearrange that as ][(){}, but the regex still looks confusing:

var  regexp =  /[][(){}]/;

See, now it looks like two character classes—an empty one, and another for the characters (){}—but again, that's just what it looks like, and the above actually works too—it's the set of characters ][(){}.

The thing is, most people don't know about this aspect of character classes, and so you'll only end up confusing others who read your code. I recommend simply escaping the ], as @vks answers:

var  regexp =  /[(){}[\]]/;

This will be understood by all.

Answer 2

[[\]({})]

You need to escape one of them so that another bracket range does not appear [ and ].

It should not form [[]==>this creates problem.use [[\] now its fine