如何定位JS中的全局变量？

Question

I'm trying to understand something with JS .. in the function below, which is the global variable? can you please help me understand this?

(function() {
  let grade = {score: 100, status: "passing"};
  age = 45;
  var salary = 45000;

Answer 1

The variable age is an implicit global because it's just mentioned on the left side of an assignment, and not explicitly declared with var or let .

In "strict" mode that would be an error.

Answer 2

Undeclared variables are always global.

Thus the variable age is the global variable.

 (function() { let grade = {score: 100, status: "passing"}; age = 45; var salary = 45000; })(); console.log(window.age); //45 console.log(window.salary);//undefined console.log(window.grade); //undefined

Answer 3

如果您没有在未声明的变量前添加 var，Javascript 将假定它是一个全局变量。