Quote JavaScript strings

utils.js

function(value) {
		
		// First we need to find which quote character to use by comparing the
		// number of times each occurs in the string.
		
		var quotes_dbl = (value.match(/"/g) || []).length;
		var quotes_sgl = (value.match(/'/g) || []).length;
		var quote = quotes_sgl <= quotes_dbl ? "'" : '"';
		var quote_code = quote.charCodeAt(0);
		
		// Next, we create a new array of substrings which contain escaped or
		// unescaped strings.
		
		var i = 0, code, code2, len = value.length, tojoin = [];
		while (len--) {
			code = value.charCodeAt(i++);
			switch (code) {
			case 8:  tojoin.push("\\b"); break;
			case 9:  tojoin.push("\\t"); break;
			case 10: tojoin.push("\\n"); break;
			case 11: tojoin.push("\\v"); break;
			case 12: tojoin.push("\\f"); break;
			case 13: tojoin.push("\\r"); break;
			case 34: /* double quote */
			case 39: /* single quote */
				tojoin.push(
					(code === quote_code ? '\\' : '') +
						String.fromCharCode(code)); break;
			case 92: tojoin.push("\\\\"); break;
			default:
				if ((code < 32) || (code > 0xfffd) ||
					(code >= 0x7f && code <= 0x9f) ||
					(code >= 0xDC00 && code <= 0xDFFF)) {
					tojoin.push("\\u" + 
						(code <= 0xf ? "000" :
							(code <= 0xff ? "00" :
								(code <= 0xfff ? "0" : ""))) + code.toString(16).toUpperCase());
				} else if (code >= 0xD800 && code <= 0xDBFF) {
					if (len < 1) {
						tojoin.push("\\u"+code.toString(16).toUpperCase());
					} else {
						code2 = value.charCodeAt(i++);
						if ((code2 < 0xDC00) || (code2 > 0xDFFF)) {
							tojoin.push("\\u"+code.toString(16).toUpperCase());
							i--;
							len++;
						} else {
							tojoin.push(String.fromCharCode(code, code2));
						}
						len--;
					}
				} else {
					tojoin.push(String.fromCharCode(code));
				}
			}
		}
		
		return quote+tojoin.join("")+quote;
	},