Summary of js pitfalls written test questions (continuously updated)

Summary of js pitfalls written test questions (continuously updated)

Ask your interviewer down. You are a qualified interviewer. The following are some mistakes-prone js test questions which will be continuously updated.

1. Evaluate the knowledge of this

 

Var length = 10 function fn () {alert (this. length)} var obj = {length: 5, method: function (fn) {fn ()//? Arguments [0] () //? } Obj. method (fn)

The pitfall here is mainly arguments. We know that except for the vertex operator, the object can be enclosed in brackets. Here, the scope of fn is arguments, that is, this = arguments in fn, only one fn parameter is passed during the call, so the length is 1.

 

2. Evaluate the understanding of pre-compilation and var

 

Var a = 1; function B () {a = 10; return; function a () {}} B (); alert ();