JS "on" function return

Question

So, I have following js function:

function check_image(imgs){             
  var img = jQuery(imgs); //This loads the image      
  img.on('load', function(e){ //success
     var display =  'display';                  
  }).on('error', function(e) { //error
     var display =  'display_none';                 
  });
    return display;         
};

Based on whether the image is available or not, I am trying to return a certain value.

I need to return the display var but I am having a hard time why it is not working.

Could someone help me out?

Thanks

Possible duplicate of [How do I return the response from an asynchronous call?](http://stackoverflow.com/questions/14220321/how-do-i-return-the-response-from-an-asynchronous-call) — Andreas, Jun 01 '16 at 07:30
it's not asynchronous call. I simply need to know how to return a value from on function. — Steve Kim, Jun 01 '16 at 07:31

score 2 · Accepted Answer · answered Jun 01 '16 at 07:50

I dont think you can directly return a value from a on function, as this only activates when the event is activated. As an alternative solution.

You can call another function in the 'on' delegates to then perform the required functionality.

function check_image(imgs){             
  var img = jQuery(imgs); //This loads the image      
  img.on('load', function(e){ //success
     updateDisplay('display', $(this));              
  }).on('error', function(e) { //error
     updateDisplay('display_none', $(this));                
  });    
};

function updateDisplay(displayVar, img) {
    if(displayVar == 'display') {

    } else if(displayVar == 'display_none') {

    }
}

Thank you. I will give it a try ! =) – Steve Kim Jun 01 '16 at 07:52 — Steve Kim, Jun 01 '16 at 07:52

score 0 · Answer 2 · answered Jun 01 '16 at 07:37

0

You return display but not define and set value for it. ( when you write var display, it mean you define a local variable and it not exist outside scope)

https://msdn.microsoft.com/library/bzt2dkta(v=vs.94).aspx

answered Jun 01 '16 at 07:37

Phúc Hoàng Trương

107
2
8

Thank you for the reply. I am aware that var display is a local variable. I want to know what the proper way of returning the inner local variable to outside so that it can be returned. Hope this makes sense. – Steve Kim Jun 01 '16 at 07:45

JS "on" function return

2 Answers2