TypeScript - replace Polish letters with English letters in a sentence

In this short article, we would like to show how to replace Polish letters with English letters in a sentence using TypeScript.

Quick solution:

const text: string = 'WSPÓŁCZYNNIK pochłaniania DŹWIĘKU';

const letters: string[] = ['ą', 'ć', 'ę', 'ł', 'ń', 'ó', 'ś', 'ź', 'ż'];
const replacement: string[] = ['a', 'c', 'e', 'l', 'n', 'o', 's', 'z', 'z'];

let result: string = text.toLocaleLowerCase();

for (let index = 0; index < letters.length; index++) {
    result = result.replaceAll(letters[index], replacement[index]);
}

console.log('before:  ' + text);   // before:  WSPÓŁCZYNNIK pochłaniania DŹWIĘKU
console.log('after :  ' + result); // after :  wspolczynnik pochlaniania dzwieku

Warnings:

• String replaceAll() was introduced in ES2021,
• String replaceAll() is supported by Node.js v16. 

Optimal solutions

In this section, you can find solutions that have quite good computational complexity.

1. replace() function-based solution

const expression: RegExp = /[ąćęłńóśźż]/gi;

const replacements: Record<string, string> = {
    'ą': 'a', 'ć': 'c', 'ę': 'e', 'ł': 'l', 'ń': 'n', 'ó': 'o', 'ś': 's', 'ź': 'z', 'ż': 'z',
    'Ą': 'A', 'Ć': 'C', 'Ę': 'E', 'Ł': 'L', 'Ń': 'N', 'Ó': 'O', 'Ś': 'S', 'Ź': 'Z', 'Ż': 'Z'
};

const replacePolishLetters = (text: string): string => {
    return text.replace(expression, (letter) => replacements[letter]);
};


// Usage example:

const text: string = 'WSPÓŁCZYNNIK pochłaniania DŹWIĘKU';
const result: string = replacePolishLetters(text);

console.log('before:  ' + text);   // before:  WSPÓŁCZYNNIK pochłaniania DŹWIĘKU
console.log('after :  ' + result); // after :  WSPOLCZYNNIK pochlaniania DZWIEKU

2. for loop-based solution

const expression: RegExp = /[ąćęłńóśźż]/gi;

const replacements: Record<string, string> = {
    'ą': 'a', 'ć': 'c', 'ę': 'e', 'ł': 'l', 'ń': 'n', 'ó': 'o', 'ś': 's', 'ź': 'z', 'ż': 'z',
    'Ą': 'A', 'Ć': 'C', 'Ę': 'E', 'Ł': 'L', 'Ń': 'N', 'Ó': 'O', 'Ś': 'S', 'Ź': 'Z', 'Ż': 'Z'
};

const replacePolishLetters = (text: string): string => {
    let result = '';
    for (let i = 0; i < text.length; ++i) {
        const entry = text[i];
        result += replacements[entry] ?? entry;
    }
    return result;
};


// Usage example:

const text: string = 'WSPÓŁCZYNNIK pochłaniania DŹWIĘKU';
const result: string = replacePolishLetters(text);

console.log('before:  ' + text);   // before:  WSPÓŁCZYNNIK pochłaniania DŹWIĘKU
console.log('after :  ' + result); // after :  WSPOLCZYNNIK pochlaniania DZWIEKU

See also

1. JavaScript - replace Polish letters with English letters in a sentence

References

1. Diacritic - Wikipedia