TypeScript - replace last 4 characters in string

In this article, we're going to have a look at how to replace the last 4 characters from string in TypeScript.

This approach allows getting substring by using negative indexes. So by using 0 and -4 indexes as the range we get <0, text.length - 4> text range. Then, we add the replacement at the end of the result string to replace the missing four characters.

xxxxxxxxxx

const text: string = 'ABCDE';

const replacement: string = '1234';

const result: string = text.slice(0, -4) + replacement;

​

console.log(result); // A1234

Output:

xxxxxxxxxx

A1234

This is an alternative approach to slice method based solution. We remove the last 4 characters to add the replacement at the end of the result string to replace the missing four characters.

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const text: string = 'ABCDE';

const replacement: string = '1234';

const result: string = text.substring(0, text.length - 4) + replacement;

​

console.log(result); // A1234

Output:

xxxxxxxxxx

A1234

There is another trick that allows replacing all characters that match expression conditions with an empty string. By using .{0,4}$ pattern we match any 4 characters (up to 4 characters) that are located at the end of the string. Then, we add the replacement at the end of the result string to replace the missing four characters.

xxxxxxxxxx

const text: string = 'ABCDE';

const replacement: string = '1234';

const result: string = text.replace(/.{0,4}$/, '') + replacement;

​

console.log(result); // A1234

Output:

xxxxxxxxxx

A1234