escaping question mark in regex javascript

Question

This is a simple question I think.

I am trying to search for the occurrence of a string in another string using regex in JavaScript like so:

 var content ="Hi, I like your Apartment. Could we schedule a viewing? My phone number is: ";

 var gent = new RegExp("I like your Apartment. Could we schedule a viewing? My", "g");

 if(content.search(gent) != -1){   
     alert('worked');     
 }

This doesn't work because of the ? character....I tried escaping it with \, but that doesn't work either. Is there another way to use ? literally instead of as a special character?

The worst part about this is that even using a string instead of a regex causes this problem, eg str.search("?") That definitely seems like a bug because that's not a regex and shouldn't be getting treated as a one. 🤦 — Synetech
– Synetech, Commented Jun 18, 2020 at 3:50

Jonathan Holloway · Accepted Answer · 2009-05-20 20:08:09Z

186

You need to escape it with two backslashes

\\?

See this for more details:

http://www.trans4mind.com/personal_development/JavaScript/Regular%20Expressions%20Simple%20Usage.htm

answered May 20, 2009 at 20:08

Jonathan Holloway

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2 Comments

Gumbo Over a year ago

… one for the regex and one for the string declration.

Geo Over a year ago

Mind blow! After years of working with regex, thought I saw everything.. But no, here you go. Double escape. Guess one day I'll see triple.

Christian C. Salvadó · Accepted Answer · 2009-05-20 20:15:06Z

31

You should use double slash:

var regex = new RegExp("\\?", "g");

Why? because in JavaScript the \ is also used to escape characters in strings, so: "\?" becomes: "?"

And "\\?", becomes "\?"

edited May 20, 2009 at 20:15

answered May 20, 2009 at 20:09

Christian C. Salvadó

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Comments

jiggy · Accepted Answer · 2009-05-20 20:14:08Z

17

You can delimit your regexp with slashes instead of quotes and then a single backslash to escape the question mark. Try this:

var gent = /I like your Apartment. Could we schedule a viewing\?/g;

answered May 20, 2009 at 20:14

jiggy

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Comments

Wiktor Stribiżew · Accepted Answer · 2020-07-30 08:07:11Z

Whenever you have a known pattern (i.e. you do not use a variable to build a RegExp), use literal regex notation where you only need to use single backslashes to escape special regex metacharacters:

var re = /I like your Apartment\. Could we schedule a viewing\?/g;
                               ^^                            ^^

Whenever you need to build a RegExp dynamically, use RegExp constructor notation where you MUST double backslashes for them to denote a literal backslash:

var questionmark_block = "\\?"; // A literal ?
var initial_subpattern = "I like your Apartment\\. Could we schedule a viewing"; // Note the dot must also be escaped to match a literal dot
var re = new RegExp(initial_subpattern + questionmark_block, "g");

And if you use the String.raw string literal you may use \ as is (see an example of using a template string literal where you may put variables into the regex pattern):

const questionmark_block = String.raw`\?`; // A literal ?
const initial_subpattern = "I like your Apartment\\. Could we schedule a viewing";
const re = new RegExp(`${initial_subpattern}${questionmark_block}`, 'g'); // Building pattern from two variables
console.log(re); // => /I like your Apartment\. Could we schedule a viewing\?/g

A must-read: RegExp: Description at MDN.

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