JavaScript: Replace all but the last number of characters with the specified mask character

JavaScript fundamental (ES6 Syntax): Exercise-85 with Solution

Mask Characters Except Last Few

Write a JavaScript program to replace all but the last number of characters with the specified mask character.

• Use String.prototype.slice() to grab the portion of the characters that will remain unmasked.
• Use String.padStart() to fill the beginning of the string with the mask character up to the original length.
• If num is negative, the unmasked characters will be at the start of the string.
• Omit the second argument, num, to keep a default of 4 characters unmasked.
• Omit the third argument, mask, to use a default character of '*' for the mask.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2
// Define the function 'mask' to mask part of a credit card number.
const mask = (cc, num = 4, mask = '*') =>
  // Convert the credit card number to a string, mask all but the last 'num' digits, and return the masked number.
  ('' + cc).slice(0, -num).replace(/./g, mask) + ('' + cc).slice(-num);

// Example usage:
console.log(mask(1234567890));  
console.log(mask(1234567890, 3));  
console.log(mask(1234567890, -4, '$')); 

Output:

******7890
*******890
$$$$567890

Visual Presentation:

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-85-1 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript program that masks all characters in a string except for the last four using a specified mask character.
• Write a JavaScript function that replaces all but the final n characters of a string with asterisks.
• Write a JavaScript program that takes a sensitive string and returns a masked version that reveals only the last few characters.

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