How to pass parameter to function using in addEventListener

Question

In the traditional way to add event listener   function getComboA sel        var value   sel options sel selectedIndex  value        lt select id  comboA  onchange  getComboA this   gt   lt option value    gt Select combo lt  option gt   lt option value  Value1  gt Text1 lt  option gt   lt option value  Value2  gt Text2 lt  option gt   lt option value  Value3  gt Text3 lt  option gt   lt  select gt    But I wanted to adapt to the addEventListener way   productLineSelect addEventListener  change  getSelection this  false    function getSelection sel       var value   sel options sel selectedIndex  value      alert value       It doesn t work because I can t pass any parameter in getSelection   as the second parameter in addEventListener method  As far as I know I can only use the function name without parenthesises   Any idea   BTW  please look at my previous question about console log doesn t work in safari 6 0 developer inspector  I can t write any output in the console  which is frustrating

User · Answer

When you use addEventListener  this will be bound automatically   So if you want a reference to the element on which the event handler is installed  just use this from within your function   productLineSelect addEventListener  change  getSelection false    function getSelection        var value   sel options this selectedIndex  value      alert value       If you want to pass in some other argument from the context where you call addEventListener  you can use a closure  like this   productLineSelect addEventListener  change   function            pass in  this   the element   and someOtherVar     getSelection this  someOtherVar      false    function getSelection sel  someOtherVar       var value   sel options sel selectedIndex  value      alert value       alert someOtherVar

User · Answer

In the first line of your JS code   select addEventListener  change   getSelection this   false     you re invoking getSelection by placing  this  behind the function reference  That is most likely not what you want  because you re now passing the return value of that call to addEventListener  instead of a reference to the actual function itself     In a function invoked by addEventListener the value for this will automatically be set to the object the listener is attached to  productLineSelect in this case   If that is what you want  you can just pass the function reference and this will in this example be select in invocations from addEventListener   select addEventListener  change   getSelection  false     If that is not what you want  you d best bind your value for this to the function you re passing to addEventListener   var thisArg     custom   object     select addEventListener  change   getSelection bind thisArg   false     The  bind part is also a call  but this call just returns the same function we re calling bind on  with the value for this inside that function scope fixed to thisArg  effectively overriding the dynamic nature of this-binding     To get to your actual question   How to pass parameters to function in addEventListener    You would have to use an additional function definition   var globalVar    global    productLineSelect addEventListener  change   function event        var localVar    local       getSelection event  this  globalVar  localVar      false     Now we pass the event object  a reference to the value of this inside the callback of addEventListener  a variable defined and initialised inside that callback  and a variable from outside the entire addEventListener call to your own getSelection function     We also might again have an object of our choice to be this inside the outer callback   var thisArg     custom   object     var globalVar    global    productLineSelect addEventListener  change   function event        var localVar    local       getSelection event  this  globalVar  localVar     bind thisArg   false

User · Answer

If the this value you want is the just the object that you bound the event handler to  then addEventListener   already does that for you   When you do this   productLineSelect addEventListener  change   getSelection  false     the getSelection function will already be called with this set to the object that the event handler was bound to   It will also be passed an argument that represents the event object which has all sorts of object information about the event   function getSelection event           this will be set to the object that the event handler was bound to        event is all the detailed information about the event       If the desired this value is some other value than the object you bound the event handler to  you can just do this   var self   this  productLineSelect addEventListener  change  function         getSelection self    false     By way of explanation    You save away the value of this into a local variable in your other event handler  You then create an anonymous function to pass addEventListener  In that anonymous function  you call your actual function and pass it the saved value of this

User · Answer

No need to pass anything in  The function used for addEventListener will automatically have this bound to the current element  Simply use this in your function   productLineSelect addEventListener  change   getSelection  false    function getSelection         var value   this options this selectedIndex  value      alert value       Here s the fiddle  http   jsfiddle net dJ4Wm     If you want to pass arbitrary data to the function  wrap it in your own anonymous function call   productLineSelect addEventListener  change   function         foo  bar       false    function foo message        alert message       Here s the fiddle  http   jsfiddle net t4Gun     If you want to set the value of this manually  you can use the call method to call the function   var self   this  productLineSelect addEventListener  change   function         getSelection call self          This ll set the  this  value inside of  getSelection  to  self     false    function getSelection         var value   this options this selectedIndex  value      alert value

[javascript] How to pass parameter to function using in addEventListener?

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