JavaScript RegExp ? Quantifier

The m? Quantifier in JavaScript is used to find the match of any string that contains zero or one occurrence of m. 

Syntax: 

/m?/ 

or

new RegExp("m?")

Syntax with modifiers:

/\m?/g 

or

new RegExp("m?", "g")

Example 1: This example matches the word e followed by zero or one occurrence of k. 

Javascript

function geek() {
    let str1 = "GeeksforGeeks@_123_$";
    let regex4 = /ek?/gi;
    let match4 = str1.match(regex4);

    console.log("Found " + match4.length
        + " matches: " + match4);
}
geek();

Output

Found 4 matches: e,ek,e,ek

Example 2: This example replaces the word 1 followed by zero or one occurrence of 2 with “@”. 

Javascript

function geek() {
    let str1 = "Geeky#12$#1";
    let regex4 = new RegExp("#12?", "gi");
    let replace = "@";
    let match4 = str1.replace(regex4, replace);
    console.log(" New string: " + match4);
}
geek();

Output

 New string: Geeky@$@

Supported Browsers: The browsers supported by RegExp ? Quantifier are listed below:

• Google Chrome
• Apple Safari
• Mozilla Firefox
• Opera
• Internet Explorer

We have a complete list of Javascript RegExp expressions, to check those please go through this JavaScript RegExp Complete Reference article.