In Javascript jQuery what does e mean

Question

I am new to JavaScript jQuery and I ve been learning how to make functions  A lot of functions have cropped up with  e  in brackets  Let me show you what I mean     this  click function e           does something       It always appears that the function doesn t even use the value of  e   so why is it there so often

User · Answer

In that example  e is just a parameter for that function  but it s the event object that gets passed in through it

User · Answer

It s a reference to the current event object

User · Answer

DISCLAIMER  This is a very late response to this particular post but as I ve been reading through various responses to this question  it struck me that most of the answers use terminology that can only be understood by experienced coders  This answer is an attempt to address the original question with a novice audience in mind    Intro  The little   e   thing is actually part of broader scope of something in Javascript called an event handling function  Every event handling function receives an event object  For the purpose of this discussion  think of an object as a  thing  that holds a bunch of properties  variables  and methods  functions   much like objects in other languages  The handle  the  e  inside the little  e  thing  is like a variable that allows you to interact with the object  and I use the term variable VERY loosely    Consider the following jQuery examples       someLink   on  click   function e      My preferred method     e preventDefault             someLink   click function e      Some use this method too     e preventDefault          Explanation     someLink  is your element selector  which HTML tag will trigger this    click  is an event  when the selected element is clicked    function e   is the event handling function  on event  object is created    e  is the object handler  object is made accessible    preventDefault    is a method  function  provided by the object    What s happening  When a user clicks on the element with the id   someLink   probably an anchor tag   call an anonymous function   function e    and assign the resulting object to a handler   e   Now take that handler and call one of its methods   e preventDefault     which should prevent the browser from performing the default action for that element   Note  The handle can pretty much be named anything you want  i e   function billybob     The  e  stands for  event   which seems to be pretty standard for this type of function   Although  e preventDefault    is probably the most common use of the event handler  the object itself contains many properties and methods that can be accessed via the event handler   Some really good information on this topic can be found at jQuery s learning site  http   learn jquery com  Pay special attention to the Using jQuery Core and Events sections

User · Answer

In jQuery e short for event  the current event object  It s usually passed as a  parameter for the event function to be fired   Demo  jQuery Events   In the demo I used e     img   on  click dblclick mouseover mouseout  function e              h1   html  Event      e type          I may as well have used event      img   on  click dblclick mouseover mouseout  function event                  h1   html  Event      event type              Same thing    Programmers are lazy we use a lot of shorthand  partly it decreases our work  partly is helps with readability  Understanding that will help you understand the mentality of writing code

User · Answer

Today I just wrote a post about  Why do we use the letters like    e    in e preventDefault     and I think my answer will make some sense     At first let us see the syntax of addEventListener  Normally it will be  target addEventListener type  listener   useCapture     And the definition of the parameters of addEventlistener are      type  A string representing the event type to listen out for       listener  The object which receives a notification  an object that implements the Event interface  when an event of the specified type   occurs  This must be an object implementing the EventListener   interface  or a JavaScript function     From MDN   But I think there is one thing should be remarked  When you use Javascript function as the listener  the object that implements the Event interface object event  will be automatically assigned to the  first parameter  of the function So if you use function e   the object will be assigned to  e  because  e  is the only parameter of the function definitly the first one    then you can use e preventDefault to prevent something      let us try the example as below    lt p gt Please click on the checkbox control  lt  p gt   lt form gt       lt label for  id-checkbox  gt Checkbox lt  label gt       lt input type  checkbox  id  id-checkbox   gt        lt  div gt   lt  form gt   lt script gt      document querySelector   id-checkbox   addEventListener  click   function e v              var e 3           var v 5           var t e v           console log t           e preventDefault            false    lt  script gt    the result will be    object MouseEvent 5 and you will prevent the click event   but if you remove the comment sign like     lt script gt         document querySelector   id-checkbox   addEventListener  click   function e v               var e 3              var v 5              var t e v              console log t               e preventDefault               false       lt  script gt    you will get   8 and an error  Uncaught TypeError  e preventDefault is not a function     at HTMLInputElement   VM409 69     Certainly the click event will not be prevented this time Because the  e  was defined again in the function   However if you change the code to    lt script gt         document querySelector   id-checkbox   addEventListener  click   function e v               var e 3              var v 5              var t e v              console log t               event preventDefault               false       lt  script gt    every thing will work propertly again   you will get 8 and the click event be prevented     Therefore   e  is just a parameter of your function and you need an  e  in you function   to receive the  event object  then perform e preventDefault    This is also the reason why you can change the  e  to any words that is not reserved by js

User · Answer

e is the short var reference for event object which will be passed to event handlers   The event object essentially has lot of interesting methods and properties that can be used in the event handlers    In the example you have posted is a click handler which is a MouseEvent     lt element selector gt   click function e           does something     alert e type     will return you click     DEMO - Mouse Events DEMO uses e which and e type  Some useful references   http   api jquery com category events   http   www quirksmode org js events properties html  http   www javascriptkit com jsref event shtml  http   www quirksmode org dom events index html  http   www w3 org TR DOM-Level-3-Events  event-types-list

User · Answer

e doesn t have any special meaning  It s just a convention to use e as function parameter name when the parameter is event   It can be     this  click function loremipsumdolorsitamet           does something     as well

User · Answer

this  click function e           does something       In reference to the above code   this  is the element which as some variable  click is the event that needs to be performed  the parameter e is automatically passed from js to your function which holds the value of   this  value and can be used further in your code to do some operation

User · Answer

The e argument is short for the event object  For example  you might want to create code for anchors that cancels the default action  To do this you would write something like      a   click function e        e preventDefault        This means when an  lt a gt  tag is clicked  prevent the default action of the click event   While you may see it often  it s not something you have to use within the function even though you have specified it as an argument

[javascript] In Javascript/jQuery what does (e) mean?

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