这是局部变量还是全局变量？

Question

I am a beginner at using JS, right now I am working on a project, where I have to explain which global and local variables I have used, I am not sure which variables are global and which are local. I know that a variable existing inside a function is a local variable, but I have the following:

onload=function(){
    var ctx=document.getElementById("canvas").getContext("2d");
};

Is my variable ctx inside the function? I am not sure, since I've used onload , I don't know if ctx is a global or local variable?

Answer 1

You are assigning a function to a variable (assigning to a variable makes no difference, it still creates the scope even if the function is not assigned), that gives ctx a functional scope. Anonymous functions are no different scope wise than a named function

Answer 2

ctx在函数内部，这意味着它不是全局变量。

Answer 3

Note that it is declared inside of a function. That means the scope of the variable is the function, which makes it local, correct. Look for where the var declaration is.

Global variables are accessible from anywhere in the program, and have the same life cycle as the rest of the code. They are declared outside of any function scope.

Answer 4

Any variable created inside a function is a local variable. That mean it would only be present until you are inside the function ie While the function is being executed and won't be accessible from outside. And any variable declared outside a function is a global function as it can be easily accessed inside the function. So in your case as your variable ctx has been declared inside a function hence it is local variable. Kindly see the link below for more detail on global variables

http://snook.ca/archives/javascript/global_variable