JavaScript - 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 JavaScript.

Quick solution:

// ONLINE-RUNNER:browser;

const text = 'WSPÓŁCZYNNIK pochłaniania DŹWIĘKU';

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

let result = text.toLocaleLowerCase();

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

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 less computational complexity.

1. replace() function-based solution

// ONLINE-RUNNER:browser;

const expression   = /[ąćęłńóśźż]/gi;

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


// Usage example:

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

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

2. for loop-based solution

// ONLINE-RUNNER:browser;

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


// Usage example:

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

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

See also

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

2. Javascript - how to replace all character that is not a letter or number with underscore and also replace Polish letters with English letters

References

1. Diacritic - Wikipedia