How callMe function works in javascript [duplicate]

Question

I am trying to use callMe in following code. But my output is coming as undefined.if I remove last console.log(myGreeting); from functopn then it printing "Hello" How it works and why its coming undefined.

var myGreeting="Hello";
function callMe(){
console.log(myGreeting);
var myGreeting = "HI";
console.log(myGreeting);
}

You aint calling callMe function, are you? No logs...running the snippet. — Ayan
– Ayan, Commented Aug 9, 2016 at 7:02
I did not. And that'w why I asked how it is work. I was not clear with msdn doc. — shanky singh
– shanky singh, Commented Aug 9, 2016 at 7:06
so it will console like first will be undefined and then second will be Hii — lazyCoder
– lazyCoder, Commented Aug 9, 2016 at 7:07

Suren Srapyan · Accepted Answer · 2016-08-09 07:09:47Z

3

JavaScript has 2 scopes, local and global. Local Scope is the every function's scope. If you have 2 variables with the same names which one is in the funciton's scope, it will first access to it's scope. So in your example the outer myGreeter is hidden for the function.Any variable that is defined as var works with hoisting. So your code translates into this one

var myGreeting="Hello";

function callMe(){

   var myGreeting; // which is undefind

   console.log(myGreeting); // undefined

   myGreeting = "HI";

   console.log(myGreeting); // HI
}

In which every variables with var keyword and functions declaration are moved to the top of the function.

For more see here https://www.sitepoint.com/demystifying-javascript-variable-scope-hoisting/

edited Aug 9, 2016 at 7:09

answered Aug 9, 2016 at 6:59

Suren Srapyan

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8 Comments

Suren Srapyan Over a year ago

@shanky singh see here

shanky singh Over a year ago

yes I am reading the doc. Thanks for answer.

shanky singh Over a year ago

@SurenSrapyan In call function why we need to declare variable. Can not we access global variable.

Suren Srapyan Over a year ago

@shankysingh Of Course we can, in your code you have declared inside the function. You can remove the inner's declaration and your code will work as you want

shanky singh Over a year ago

That I declare after first console.log(myGreeting); . You declare that one before which is coming as undefined. Any how I am getting undefined.

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