stringformat.js

// Based on http://www.diveintojavascript.com/projects/sprintf-for-javascript

String.prototype.format = function() {
	var i = 0, a, f = this, o = [], m, p, c, x, s = '';
	while (f) {
		if (m = /^[^\x25]+/.exec(f)) {
			o.push(m[0]);
		}
		else if (m = /^\x25{2}/.exec(f)) {
			o.push('%');
		}
		else if (m = /^\x25(?:(\d+)\$)?(\+)?(0|'[^$])?(-)?(\d+)?(?:\.(\d+))?([b-fosuxX])/.exec(f)) {
			if (((a = arguments[m[1] || i++]) == null) || (a == undefined)) {
				throw('Too few arguments.');
			};
			if (/[^s]/.test(m[7]) && (typeof(a) != 'number')) {
				throw('Expecting number but found ' + typeof(a));
			};
			switch (m[7]) {
				case 'b': a = a.toString(2); break;
				case 'c': a = String.fromCharCode(a); break;
				case 'd': a = parseInt(a); break;
				case 'e': a = m[6] ? a.toExponential(m[6]) : a.toExponential(); break;
				case 'f': a = m[6] ? parseFloat(a).toFixed(m[6]) : parseFloat(a); break;
				case 'o': a = a.toString(8); break;
				case 's': a = ((a = String(a)) && m[6] ? a.substring(0, m[6]) : a); break;
				case 'u': a = Math.abs(a); break;
				case 'x': a = a.toString(16); break;
				case 'X': a = a.toString(16).toUpperCase(); break;
			};
			a = (/[def]/.test(m[7]) && m[2] && a >= 0 ? '+'+ a : a);
			c = m[3] ? m[3] == '0' ? '0' : m[3].charAt(1) : ' ';
			x = m[5] - String(a).length - s.length;
			p = m[5] ? this.str_repeat(c, x) : '';
			o.push(s + (m[4] ? a + p : p + a));
		}
		else {
			throw('Unknown error');
		};
		f = f.substring(m[0].length);
	};
	return o.join('');
	
  function str_repeat(i, m) {
  	for (var o = []; m > 0; o[--m] = i);
  	return o.join('');
  };
	
};