How to replace characters except last with a mask character in JavaScript?

Front End Technology Javascript Web Development

JavaScript has a built-in function called replace() that can be used to replace characters in a string. This function takes two arguments: the first argument is the character or characters to be replaced, and the second argument is the character or characters to replace them with.

Syntax

Following is the syntax to replace characters except last with a specified mask −

str.replace(/.(?=.)/g, "x");

The first argument to the replace() method is character/s to be replaced. We pass a regular expression for all characters except last as the first argument to the replace method. All characters except the last are replaced with a specified mask ‘x’.

Algorithm

STEP 1 − Create a variable named str and assign the sting to it.
STEP 2 − Replace the characters using the String replace() method. Use the syntax discussed above.
STEP 3 − Display the string with replaced characters.

Example 1

In the program below, we replace all characters except the last one with a specified mask character ie. “x”. We use the above-defined syntax of the replace method.


<html>
<body>
   <div id="result1"></div>
   <div id="result2"></div>
   <script>
      var str = "Hello world";
      document.getElementById("result1").innerHTML = "Original String: " + str
      var newStr = str.replace(/.(?=.)/g, "x");
      document.getElementById("result2").innerHTML = "String after replacement: " + newStr
   </script>
</body>
</html>

In the example above, the replace() function replaces all characters except the last one with the character "x".

If you want to replace only the first occurrence of a character, you can use the replace() function like this −

var str = "Hello world!";
var newStr = str.replace("l", "x", 1);

Example 2

In the example below, we replace all characters except last with a mask character. We take the string and mask character from the user.


<!doctype html>
<html>
<head>
   <title>Examples</title>
</head>
<body>
   <p>Enter String: </p>
   <input type="text" id="myStr" value="">
   <p>Enter mask character: </p>
   <input type="text" id="myMask" value="">
   <p> String after replacement:</p>
   <div id="result"></div>
   <button onclick="replaceStr()">Replace</button>
   <script>
      function replaceStr() {
         var str = document.getElementById("myStr").value;
         var mask = document.getElementById("myMask").value;
         var newStr = str.replace(/.(?=.)/g, mask);
         document.getElementById("result").innerHTML = newStr
      }
   </script>
</body>
</html>

There are many benefits of using the replace() function. First, it is very easy to use. Second, it is very versatile and can be used to replace characters in a string with any other character or characters.

In conclusion, the replace() function is a very useful function that can be used to replace characters in a string. It is very easy to use and is very versatile.