javascript中undefined,null,NaN等的区别用法实例详解:js中undefined,null,NaN的区别1.类型分析：js中的数据类型有undefined,boolean,number,string,object等5种，前4种为原始类型，第5种为引用类型。var a1; var a2 = true; var a3 = 1; var a4 = "Hello";