Question

162

How to escape and unescape quotes in JavaScript?

rated 0 times [ 165] [ 3] / answers: 1 / hits: 18905 / 11 Years ago, thu, january 30, 2014, 12:00:00

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?

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tomas

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answered 11 Years ago dexter · Accepted Answer

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.