How to Pass JavaScript Function as Parameter

1. Pass a General JavaScript Function as a Parameter
2. Pass Both Function and Value to a JavaScript Function

In JavaScript, passing a function as a parameter to another function is similar to passing values. The way to pass a function is to remove the parenthesis () of the function when you assign it as a parameter.

In the following sections, a function pass is demonstrated as a parameter.

Pass a General JavaScript Function as a Parameter

For this drive, we will initiate a function func2 with a code body and directly pass it to the function func1. Later, after assigning func2 to func1, we will call the func2 aka function_parameter.

function func1(function_parameter) {
  function_parameter();
}

function func2() {
  console.log('okay!');
}

func1(func2);

Output:

The example depicts that func2 is passed to func1. And when func1 is called, it checks its argument (func2) and previews the code fenced by func2.

Pass Both Function and Value to a JavaScript Function

JavaScript allows the passing of function and value together in another function, making functions more dynamic. This declaration will require an input of integer, bool, string, or maybe even a function, and the other parameter is the function parameter.

We will see two examples of this category.

Function and value as function parameters:

function pass(value) {
  return ('Hello ' + value);
}

function receive_pass(x, func) {
  console.log(func(x));
}

receive_pass('David', pass);

Output:

Two functions as function parameters:

function pass1(value) {
  return ('Hello ' + value);
}

function pass2() {
  return (' Howdy!');
}

function receive_pass(func1, func2) {
  console.log(func1('world!') + func2());
}

receive_pass(pass1, pass2);

Output:

As per the code instances, JavaScript takes functions as a parameter like any other regular data type. The core difference is when a function is called in the parenthesis of the argument, functions should be removed; otherwise, this can cause an error while running.