js实现format

var stringFormat = function(tpl ,arr){
var newStr = tpl;
for (var key in arr) {
while (newStr.indexOf('{' +key+ '}') >= 0) {
newStr = newStr.replace('{' + key+ '}',arr[key]);
}
};
return newStr;
};

String.prototype.format=function() {
var formatted = this;
for (var i = 0; i < arguments.length; i++) {
var regexp = new RegExp('\\{'+i+'\\}', 'gi');
formatted = formatted.replace(regexp, arguments[i]);
}
return formatted;
};