javascript - What is the parameter to use for event? how do i know? -

element.onkeypress = function(e) {                     if(e.keycode) {                         element.keycode = e.keycode;                     } else {                         element.keycode = e.charcode;                     }                 }; 

also in java script , there also

<input onchange="a(event)"/> <script> function a(event) {      alert(event.target.value); } </script> 

as parameter receiving, how know if must put event parameter instead of e? second example wont work if it's parameter other event aren't both javascript?

when bind event handler using on* property or addeventlistener, event object passed first argument. name usual when writing function expression or function declaration. normal restrictions on can name arguments apply (i.e. must valid identifier names). event, e , evt common names variable.

when bind event handler using on* attribute, writing function body (i.e. function (event) { , } implied. event object available in event variable.