Convert Integer to Variable-Length Quantity (VLQ) in JavaScript

variable-length-quantity.js

// Integer to variable-length quantity (VLQ)
// This is partialy used by ASN.1 for OBJECT IDENTIFIERS
let intToVQL = function(n) {
	// If simple form, just return (for simplecity)
	// Next line can be removed and the results will be the same
	if (n < 128) return new Uint8Array([n]);

	// Initial array of bytes
	let value = [];

	// Convert number to array of bits
	n = n.toString(2);
	// Pad bits with zero to have a length multiple of 7
	while (n.length % 7 != 0) n = '0' + n;
	// Split stream to groups of 7 bits
	n = n.match(/.{1,7}/g);

	// For each group add bit 1 infort of the group exept from the last one
	// then convert it back to number and push it into our array
	for (let i = 0; i < n.length; i++) {
		value.push(parseInt((i < n.length - 1 ? '1' : '0') + n[i], 2));
	}

	// Convert to byte array and return
	return new Uint8Array(value); 
}

// Resources used to learn about the format
// https://stackoverflow.com/questions/5929050/how-does-asn-1-encode-an-object-identifier
// https://en.wikipedia.org/wiki/Variable-length_quantity
// https://docs.microsoft.com/en-us/windows/win32/seccertenroll/about-object-identifier?redirectedfrom=MSDN