Replace substring which contains backslash using RegExp function javascript

Question

I am trying to write a function which replaces certain words with abbreviations. For example I have the string:

str="Calculate $2\\cdot 2$"

in which I want to replace

"\\cdot" 

with

"*" 

My code looks like this:

str = str.replace(RegExp("\\cdot",'g'),"*");

And the result is

str = "Calculate $2\\cdot 2$"

And I need to use the RegExp function because I have a whole list of words which I want to replace with abbreviations. I know that

str = str.replace(/\\cdot/g),"*");

works. But I don't understand why RegExp doesn't.

Answer 1

You need to escape the slash character when defining a String and once again for the regular expression. If you just escape the slash once in a String, the resulting regex would like this: \cdot. If you define the regular expression directly with the slash notation (/regex/), you would only need to escape it once, because there is no String.

var str = "Calculate $2\\cdot 2$";
str = str.replace(RegExp("\\\\cdot",'g'),"*");
console.log(str);

---

If you want to generically prepend all the regex special characters with a slash, you can use the following solution, which relies on this answer. You still have to escape the backslash once, because it is part of a String. If you get your String from somewhere, it will be correctly escaped. It's only necessary, if you explicitly write the String into the code (var string = "string";).

var str = "Calculate $2\\cdot 2$";
var regex = "\\cdot";
str = str.replace(RegExp(escapeRegExp(regex), 'g'),"*");
console.log(str);

function escapeRegExp(str) {
    return str.replace(/[\-\[\]\/\{\}\(\)\*\+\?\.\\\^\$\|]/g, "\\$&");
}