printf for js

format.js

register = {
    "beep": "boop"
};

function format(str) {
  var argi = 0;
  var args = arguments;
  return str.replace(/(%\w{1}$)|(<.+>)/g, 
    function (match, specifier, interpol) {
      if (specifier) {
        var type = specifier.replace("%", "");
        var arg = args[++argi];
        switch (type) {
          case 'd': return Number(arg);
          case 'j': return JSON.stringify(arg);
        }
        return String(arg);
      }
      if (interpol) {
        var key = interpol.replace(/<|>/g, "");
        return register[key] || key;
      }
  });
}
console.log(format("%s", 1));
console.log(format("<beep>  %s", 1));