JavaScript - How to Mask All Characters Except the Last?

Here are the different methods to replace characters except the last with the specified mask character in JavaScript.

1. Using slice() and repeat() Methods

Use slice() to get the last character of the string and repeat() to mask the rest of the characters.

let s = "123456789";
let maskChar = "*";
let masked = maskChar.repeat(s.length - 1) + s.slice(-1);

console.log(masked);

********9

• maskChar.repeat(s.length - 1) creates a string of * characters for all but the last character.
• s.slice(-1) gets the last character of the string.
• The result is a concatenation of the masked part and the last character.

2. Using substring() and repeat() Methods

This approach is quite similar to the first, but instead of slice(), we use substring() to get the last character.

let s = "9876543210";
let maskChar = "#";
let masked = maskChar.repeat(s.length - 1) + s.substring(s.length - 1);

console.log(masked);

#########0

• maskChar.repeat(s.length - 1) repeats the mask character for all but the last character.
• s.substring(s.length - 1) extracts the last character.

3. Using Array.map() and join()

In this we convert the string into an array, masking all but the last character, and then using join() to form the final string.

let s = "abcdefgh";
let maskChar = "$";
let masked = s.split('').map((char, idx) => 
	idx === s.length - 1 ? char : maskChar).join('');

console.log(masked);

$$$$$$$h

• s.split('') converts the string into an array of characters.
• map() is used to replace each character with the mask unless it's the last character.
• join('') reassembles the array back into a string.

4. Using replace() with a Regular Expression

This approach uses a regular expression to match all characters except the last one and replace them with the mask character.

let s = "abcdefg";
let maskChar = "&";
let masked = s.replace(/.(?=.{1})/g, maskChar);

console.log(masked); 

&&&&&&g

• The regex /(.?=.{1})/g matches all characters except the last one.
• replace() replaces the matched characters with the mask character (&).

5. Using for Loop with String Concatenation

This is a more manual approach where a loop is used to iterate over the string and build the masked string.

let s = "987654321";
let maskChar = "+";
let masked = "";

for (let i = 0; i < s.length - 1; i++) {
    masked += maskChar;
}
masked += s[s.length - 1];

console.log(masked);

++++++++1

• The loop iterates through the string and adds the mask character for each character except the last one.
• The last character is appended directly after the loop.

6. Using StringBuilder Approach (Manual String Concatenation)

For larger strings or performance-sensitive situations, manually building a string using string concatenation can be a choice.

let s = "hello123";
let maskChar = "X";
let masked = "";

for (let i = 0; i < s.length - 1; i++) {
    masked += maskChar;
}
masked += s.charAt(s.length - 1);

console.log(masked); 

XXXXXXX3

• Concatenate X for all characters except the last one using a loop.
• charAt(s.length - 1) retrieves the last character.

khushindpatel

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Article Tags :

• JavaScript
• Web Technologies
• javascript-string
• javascript-functions
• JavaScript-DSA
• JavaScript-RegExp
• JavaScript-Questions

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