情况一: ```js var bb=1; function aa(bb){ bb=2; console.log(bb); } aa(bb);//2 console.log(bb);//1 ``` 情况二: ```js var bb=1; function aa(){ bb=2; console.log(bb); } aa(bb);//2 console.log(bb);//2 ``` 情况三: ```js var bb={c:1}; function aa(bb){ bb={c:2}; console.log(bb); } aa(bb);//Object{c:2} console.log(bb);//Object{c:1} ``` 情况三: ```js var bb={c:1}; function aa(bb){ bb.c=2; console.log(bb); } aa(bb);//Object{c:2} console.log(bb);//