If statement within JavaScript function not working

Question

I have the following function

var VisibilityNewDevice = 1
function visibilityNewDevice() {
    if (VisibilityNewDevice === 1) {
         toggleVisibility('buttonPressesTable'),
         toggleVisibility('IconMinimize'),
         toggleVisibility('IconSync'); 
         var VisibilityNewDevice = 0;
    }
}

Which if I call visibilityNewDevice() I get undefined returned and doesn't run the code. However if I run the like this

if (VisibilityNewDevice === 1) {
    toggleVisibility('buttonPressesTable'),
    toggleVisibility('IconMinimize'), 
    toggleVisibility('IconSync'); 
    var VisibilityNewDevice = 0;
}

It works fine. I'm confused why the function doesn't work, but when I run the if statement it works fine.

var hoisting: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… — Jay Harris
– Jay Harris, Commented Jul 17, 2015 at 21:54

Sarath Chandra · Accepted Answer · 2015-07-17 21:56:33Z

2

Your function tries to define the variable again.

Your

var VisibilityNewDevice = 0;

at the end of the function should be

VisibilityNewDevice = 0;

answered Jul 17, 2015 at 21:56

Sarath Chandra

1,87621 silver badges40 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Jay Harris · Accepted Answer · 2015-07-17 22:20:40Z

The answer is to simply remove the var inside the function

You write

var VisibilityNewDevice = 1
function visibilityNewDevice() {
  // expecting: 1 === 1
  if (VisibilityNewDevice === 1) {
     ...
     var VisibilityNewDevice = 0;
  }
}

Javascript compiles

var VisibilityNewDevice = 1
function visibilityNewDevice() {
    var VisibilityNewDevice = undefined;

    // undefined === 1
    if (VisibilityNewDevice === 1) {
     ... 
     VisibilityNewDevice = 0;
   }
}

Notice your var is hoisted at the top, that goes for any var you create inside the function. That hoisted var will overwrite any global var with the same name when the program enters the function.

Comments

c-smile · Accepted Answer · 2015-07-17 21:56:08Z

1

By having

var VisibilityNewDevice;

you've declared local variable VisibilityNewDevice inside the function. By having

var VisibilityNewDevice = 0;

you are setting that local variable to zero. Not the outer one as you need.

answered Jul 17, 2015 at 21:56

c-smile

27.6k8 gold badges66 silver badges91 bronze badges

Comments

abs · Accepted Answer · 2015-07-17 22:01:10Z

0

This is call variable hoisting.

var x = 1;

function test(){
   console.log(x);
   var x = 3;
}

test();

this is same as

function test(){
       var x;
       console.log(x);
       x = 3;
    }

answered Jul 17, 2015 at 22:01

abs

8016 silver badges15 bronze badges

Collectives™ on Stack Overflow

If statement within JavaScript function not working

5 Answers 5

Comments

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

Comments

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related