jquery原代码:isType()
class2type = {}; toString = Object.prototype.toString; type: function( obj ) { return obj == null ? String( obj ) : class2type[ toString.call(obj) ] || "object"; }, isFunction: function( obj ) { return jQuery.type(obj) === "function"; }, isArray: Array.isArray || function( obj ) { return jQuery.type(obj) === "array"; }, // A crude way of determining if an object is a window isWindow: function( obj ) { return obj && typeof obj === "object" && "setInterval" in obj; }, isNaN: function( obj ) { return obj == null || !rdigit.test( obj ) || isNaN( obj ); },