PRDV401: Introduction to JavaScript I

When using an immediately-invoked function expression, void can be used to force the function keyword to be treated as an expression instead of a declaration.

void function iife() {
  console.log("Executed!");
}();

// Output: "Executed!"

Executing the above function without the void keyword will result in an Uncaught SyntaxError.

When a browser follows a javascript: URI, it evaluates the code in the URI and then replaces the contents of the page with the returned value, unless the returned value is undefined. The void operator can be used to return undefined. For example:

<a href="javascript:void(0);">
  Click here to do nothing
</a>

<a href="javascript:void(document.body.style.backgroundColor='green');">
  Click here for green background
</a>

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

Arrow functions introduce a short-hand braceless syntax that returns an expression. This can cause unintended side effects by returning the result of a function call that previously returned nothing. To be safe, when the return value of a function is not intended to be used, it can be passed to the void operator to ensure that (for example) changing APIs do not cause arrow functions' behaviors to change.

button.onclick = () => void doSomething();