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JavaScript | RegExp ? Quantifier

  • Difficulty Level : Basic
  • Last Updated : 31 Dec, 2019

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




<!DOCTYPE html>
<html>
  
<head>
    <title>
        JavaScript RegExp ? Quantifier
    </title>
</head>
  
<body style="text-align:center">
      
    <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>
</body>
  
</html>                    

Output:
Before Clicking the button:
plus
After Clicking the button:
plus

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




<!DOCTYPE html>
<html>
  
<head>
    <title>
        JavaScript RegExp ? Quantifier
    </title>
</head>
  
<body style="text-align:center">
      
    <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>
</body>
  
</html>                    

Output:
Before Clicking the button:
plus
After Clicking the button:
plus

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

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



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