Differences between Javascript regexp literal and constructor
javascript, regex
Solution
There are two problems:
The `/` are not part of the expression. They are delimiters, marking a regex literal. They have to be removed if you use `RegExp`, otherwise they match a slash literally.
Secondly, the backslash is the escape character in string literals. To create a literal `\` for the expression, you have to escape it in the string.
Thus, the equivalent would be:
new RegExp("rt:([^@]+)@(\\d+)")
Especially the escaping makes expression a bit more difficult to write if you want to use `RegExp`. It is actually only needed if you want to create expression dynamically, that is, if you want to include text stored in a variable for example. If you have a fixed expression, a literal `/.../` is easier to write and more concise.
Problem
We recently had a bug, after a fellow developer changed a RegExp literal into a constructor call, and I was wondering why there is any difference at all. The exact code was ``` var parts = new RegExp("/rt:([^@]+)@(\d+)/").exec(tag); ``` vs the original of ``` var parts = /rt:([^@]+)@(\d+)/.exec(tag); ``` When `tag` is, for example `rt:60C1C036-42FA-4073-B10B-1969BD2358FB@00000000077`, the first (buggy) call returns `null`, while the second one returns`["rt:60C1C036-42FA-4073-B10B-1969BD2358FB@00000000077", "60C1C036-42FA-4073-B10B-1969BD2358FB", "00000000077"]` Needless to say, I reverted the change, but I'd like to know why is there such a difference in the first place.