创建正则表达式以替换具有相同字符的字符串的每个匹配字符

Question

In my application, I have an alphanumeric string being passed into my function. This string is typically 17 characters, but not always. I'm trying to write a regex that matches all but the last 4 characters in the string, and replaces them with X (to mask it).

For example

Input: HGHG8686HGHG8686H

Output: XXXXXXXXXXXXX686H

The Regex I wrote to perform the replace on the string is as follows

[a-zA-Z0-9].{12}

Code:

const maskedString = string.replace(/[a-zA-Z0-9].{12}/g, 'X');

The issue I'm having is that it's replacing all but the last 4 characters in the string with just that single X. It doesn't know to do that for every matched character. Any ideas?

Answer 1

you can use a function inside replace to do this, something like this will do:

 var str = "HGHG8686HGHG8686H" var regexp = /[a-zA-Z0-9]+(?=....)/g; var modifiedStr = str.replace(regexp, function ($2) { return ('X'.repeat($2.length +1)); }); console.log(modifiedStr); 

Answer 2

Look ahead ( ?= ) to make sure there are at least four following characters.

 const regex = /.(?=....)/g; // ^ MATCH ANYTHING // ^^^^^^^^ THAT IS FOLLOWED BY FOUR CHARS function fix(str) { return str.replace(regex, 'X'); } const test = "HGHG8686HGHG8686H"; // CODE BELOW IS MERELY FOR DEMO PURPOSES const input = document.getElementById("input"); const output = document.getElementById("output"); function populate() { output.textContent = fix(input.value); } input.addEventListener("input", populate); input.value = test; populate(); 

 <p><label>Input: </label><input id="input"></p> <p>Output: <span id="output"></span></p> 

A non-regexp solution:

 const test = "HGHG8686HGHG8686H"; function fix(str) { return 'X'.repeat(str.length - 4) + str.slice(-4); } console.log(fix(test)); 

You will not find String#repeat in IE.

Answer 3

The simple version: (Easier to read)

const maskedString = string.replace(/(.{4})$|(^(..)|(.))/g, 'X\1'); // or X$1

Now using: [a-zA-Z0-9]

const maskedString = string.replace(/([a-zA-Z0-9]{4})$|(^([a-zA-Z0-9]{2})|([a-zA-Z0-9]{1}))/g, 'X\1'); // or X$1

Note: The reason i match on the START PLUS TWO characters is to offset the first match. (The final 4 characters that are appended at the end.)

Answer 4

You can achieve using following method:

  var str = "HGHG8686HGHG8686H" var replaced='' var match = str.match(/.+/) for(i=0;i<match[0].length-4;i++){ str = match[0][i] replaced += "X" } replaced += match[0].substr(match[0].length-4) console.log(replaced);