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 occurrences of k. 

html

<h1 style="color:green">
    GeeksforGeeks
</h1>

<h2>RegExp ? Quantifier</h2>

<p>Input String: GeeksforGeeks@_123_$</p>

<button onclick="geek()">
    Click it!
</button>

<p id="app"></p>

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

        document.getElementById("app").innerHTML
                = "Found " + match4.length
                + " matches: " + match4;
    }
</script>

Output:

JavaScript RegExp ? Quantifier

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

html

<h1 style="color:green">
    GeeksforGeeks
</h1>

<h2>RegExp ? Quantifier</h2>

<p>String: Geeky#12$#1</p>

<button onclick="geek()">
    Click it!
</button>

<p id="app"></p>

<script>
    function geek() {
        var str1 = "Geeky#12$#1";
        var regex4 = new RegExp("#12?", "gi");
        var replace = "@";
        var match4 = str1.replace(regex4, replace);
        document.getElementById("app").innerHTML =
            " New string: " + match4;
    }
</script>

Output:

JavaScript RegExp ? Quantifier

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.

We have a Cheat Sheet on Javascript where we covered all the important topics of Javascript to check those please go through Javascript Cheat Sheet-A Basic guide to JavaScript.