stringToBigInt.js

// https://stackoverflow.com/questions/40958727/javascript-generate-unique-number-based-on-string

(() => {
	function base0xFFFFtoBigInt(str) {
		const base = BigInt(0xFFFF);
		let result = BigInt(0);
		let pow = 0;
		let i = str.length;
		while (i-->0) {
			const charCode = BigInt(str.charCodeAt(i));
			result += charCode * (base ** BigInt(pow++));
		}
		return result
	}
	function bigIntToBase0xFFFF(int) {
		int = BigInt(int);
		const base = BigInt(0xFFFF);
		let result = '';
		while (int) {
			let rest = int % base;
			result = String.fromCharCode(Number(rest)) + result;
			int -= rest;
			int /= base;
		}
		return result;
	}
	const input = '_';
	const nr = base0xFFFFtoBigInt(input);
	console.log('input: %s; output: %s', input, nr)
	const str = bigIntToBase0xFFFF(nr);
	console.log(str,'!!!');
})();