javascript void
snippet in javascript

javascript.void(0)

user9013

<a href="javascript:void(0);" ondblclick="alert('Welcome')"> Double click Please </a>

javascript void

user4951

<a href="JavaScript:void(0)">Dead Link</a>

javascript void(0) href

user3179

<!DOCTYPE html>
<html>
   <head>
      <title>Understanding JavaScript void(0)</title>
   </head>
   <body>
      <a href="javascript:void(0);" ondblclick="alert('Click it twice!')">Click me not once, but twice.</a>
   </body>
</html>

where use javascript:void(0)

user9414

<a href="javascript:void(0)">Link</a>

href javascript void

user2645

The void operator evaluates the given expression and then returns undefined.

The void operator is often used merely to obtain the undefined primitive value,
usually using “void(0)” (which is equivalent to “void 0”). In these cases,
the global variable undefined can be used instead (assuming it has not been
assigned to a non-default value).

An explanation is provided here: void operator.

The reason you’d want to do this with the href of a link is that normally,
a javascript: URL will redirect the browser to a plain text version
of the result of evaluating that JavaScript. But if the result is undefined,
then the browser stays on the same page. void(0) is just a short and 
simple script that evaluates to undefined.