/**
* 格式化字符串中的表达式:{0}、{1}、{2}...
*/
String.format = (function() {
var re = /\{(\d+)\}/g;
return function() {
var str = arguments[0],
args = Array.prototype.slice.call(arguments, 1);
if (str == null) return;
return str.replace(re, function(m, i) {
return args[i] != null ? args[i] : m;
});
};
})();