Converts hexadecimal-formatted strings to numbers and back

hexconverter.js

Number.prototype.toHex = function (padSize) {
	if (padSize == undefined) padsize = 1;
	var hex = this.toString(16).toUpperCase();
	while (padSize > hex.length) {
		hex = "0" + hex;
	}
	return hex;
};

String.prototype.toHex = function () {
	var bytes, n, len, charCode;
	
	len = this.length;
	bytes = [];
	
	for (n = 0; n < len; n++) {
		charCode = this.charCodeAt(n);
		// limit to utf-8 visible characters
		if (0x1F < charCode && charCode < 0x7F) bytes.push(charCode.toHex(2));
	}
	return bytes.join("");
};

var hex_checksum = function (hex) {
	var pair, tc, lsb,
		sum = 0,
		h = [],
		d = [];
	
	if (typeof hex === "string") {
		hex.replace(/^0x/i, "");
		for (var i = 0, len = hex.length; i < len; i+=2) {
			pair = hex.substr(i, 2);
			h.push(pair);
			dec = parseInt(pair, 16);
			d.push(dec);
			sum += dec;
		}
	} else if (typeof hex === "number") {
		return;
	} else {
		return null;
	}
	
	//console.log(h);
	//console.log(d);
	//console.log("Sum of Pairs:", sum.toHex());
	//tc = ~sum + 0x01;
	tc = (sum ^ 0xFF) + 0x01;
	//console.log("Two's Complement of sum of pairs:", tc.toHex());
	lsb = tc & 0xFF;
	//return lsb < 0x10 ? "0" + lsb.toHex() : lsb.toHex();
	return lsb;
};

var makeHex = function (maxLen, memStart, data) {
	var lines, lineData, byteCount, address;
	
	maxLen = Math.abs(parseInt(maxLen));
	memStart = Math.abs(parseInt(memStart));
	data.replace(/^0x/i, "");
	lines = [];
	address = memStart;
	
	if (data.length % 2) { console.error("Data should have an even number of characters."); return; }
	
	while (data.length > 0) {
		lineData = data.substr(0, 2 * maxLen);
		byteCount = (lineData.length >> 1).toHex(2);
		str = byteCount + address.toHex(4) + "00" + lineData;
		lines.push(":" + str + hex_checksum(str).toHex(2));
		data = data.substr(2 * maxLen);
		address += maxLen;
	}
	lines.push(":00000001FF");
	return lines.join("\n");
};