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What does “javascript:void(0)” mean?

I want to ask a few questions regarding javascript:void(0)

<input type='submit' name='btn' value='submit' onClick='javascript:void(0)' />

Can you please explain void(0) – is it a built-in function? Does the keyword javascript represent that the code is written in javascript? If there is anything weird that you know about it, please share it with me. Thank you.

Answer 1

void():

This operator allows inserting expressions that produce side effects
into places where an expression that evaluates to undefined is
desired.

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).
Note, however, that the javascript: pseudo protocol is discouraged over other alternatives, such as unobtrusive event handlers.

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