How to escape and unescape quotes in JavaScript?
javascript, regex, replace, string
Solution
The problem is that you're using the `RegExp` constructor, which accepts a string, rather than using a regular expression literal. So in this line in your unescape:
return string.replace(new RegExp('\\"', 'g'),'"');
...the `\\` is interpreted by the JavaScript parser as part handling the string, resulting in a single backslash being handed to the regular expression parser. So the expression the regular expression parser sees is `\"`. The backslash is an escape character in regex, too, but `\"` doesn't mean anything special and just ends up being `"`. To have an actual backslash in a regex, you have to have two of them; to do that in a string literal, you have to have four (so they survive both layers of interpretation).
Unless you have a very good reason to use the `RegExp` constructor (e.g., you have to use some varying input), always use the literal form:
var utility = {
escapeQuotes: function(string) {
return string.replace(/"/g, '\\"');
},
unescapeQuotes: function(string) {
return string.replace(/\\"/g, '"');
}
};
It's a lot less confusing.
Problem
Here's a short piece of code: ``` var utility = { escapeQuotes: function(string) { return string.replace(new RegExp('"', 'g'),'\\"'); }, unescapeQuotes: function(string) { return string.replace(new RegExp('\\"', 'g'),'"'); } }; var a = 'hi "'; var b = utility.escapeQuotes(a); var c = utility.unescapeQuotes(b); console.log(b + ' | ' + c); ``` I would expect this code to work, however as a result I receive: ``` hi \" | hi \" ``` If I change the first parameter of the new RegExp constructor in the unescapeQuotes method to 4 backslashes everything starts working as it should. ``` string.replace(new RegExp('\\\\"', 'g'),'"'); ``` The result: ``` hi \" | hi " ``` Why are four backslashes needed as the first parameter of the new RegExp constructor? Why doesn't it work with only 2 of them?