I am studying about RegExp but everywhere I can see two syntax
And if with modifiers then what is the use of additional slash (
I am not getting any bug with these two but I wonder is there any difference between these two. If yes then what is it and which is best to use?
The key difference is that literal REGEX can't accept dynamic input, i.e. from variables, whereas the constructor can, because the pattern is specified as a string.
Say you wanted to match one or more words from an array in a string:
var words = ['foo', 'bar', 'orange', 'platypus']; var str = "Foo something nice orange what a lovely platypus"; str.match(new RegExp('\\b('+words.join('|')+')\\b'));
This would not be possible with a literal
/pattern/, as anything between the two forward slashes is interpreted literally.
Note also the need to double-escape (i.e.
\\) special characters when specifying patterns in this way, because we're doing so in a string - the first backslash must be escaped by the second so one of them makes it into the pattern. If there were only one, it would be interpreted by JS's string parser as an escaping character, and removed.
As you can see, the
RegExp constructor syntax requires string to be passed.
\ in the string is used to escape the following character. Thus,
new RegExp("\s") // This gives the regex `/s/` since s is escaped.
will produce the regex
Note: to add modifiers/flags, pass the flags as second parameter to the constructor function.
/\s/ - the literal syntax, will produce the regex which is predictable.
RegExp constructor syntax allows to create regular expression from the dynamically.
So, when the regex need to be crafted dynamically, use
RegExp constructor syntax otherwise use regex literal syntax.
There are 2 ways of defining regular expressions.
The literal is the best to use with known regular expressions, while the constructor is better for dynamically constructed regular expressions such as those from user input.
You could use any of the two and they will be handled in exactly the same way..
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