Example Node.js 4.0.0/ES6 : Vigenère cipher Class

vegenere.class.js

'use strict';

class VigenereCipher {
	constructor(key) {
		this.key = key;
	}

	crypt(text) {
		var cypher = '';
		text = text.toUpperCase();
		for(let i =0; i<text.length; i++) {
			if(text[i] === " ") {
				cypher += text[i];
			} else {
				cypher += String.fromCharCode(((text.charCodeAt(i) + this.key.charCodeAt(i))%26)+65)
			}
		}
		return cypher;
	};

	decrypt(cypher) {
		var text = '';
		for(let i =0; i<cypher.length; i++) {
			if(cypher[i] === " ") {
				text += cypher[i];
			} else {
				text += String.fromCharCode(((((cypher.charCodeAt(i) - this.key.charCodeAt(i)) % 26)+26)%26)+65)
			}
		}
		return text;
	}
}

var vCrypt = new VigenereCipher('M USIQU EMUSIQU EM USIQU EMUSI QU EMUSIQU');
console.log(vCrypt.crypt('j adore ecouter la radio toute la journee'));
console.log(vCrypt.decrypt('V UVWHY IOIMBUL PM LSLYI XAOLM BU NAOJVUY'));