how to use function in javascript

JavaScript
A function is a reusable block of code that allows you to 
input specific values. To specify the values you need to call
the function by typing the name along with the desired values
spaced by commas.

function myFunction(value1, value2) {
	return value1 + value2;
}

myFunction(10, 5);




Now the function will return 15./* Declare function */
function myFunc(param) {
  // Statements 
}
Source

Also in JavaScript: