JavaScript Enlightenment

Chapter 4. Function()

Conceptual Overview of Using Function() Objects

A function is a container of code statements that can be invoked using the parentheses () operator. Parameters can be passed inside of the parentheses during invocation so that the statements in the function can access certain values when the function is invoked.

Below, we create two versions of an addNumbers function object—one using the new operator and another using the more common, literal pattern. Both are expecting two parameters. In each case, we invoke the function, passing parameters in the parentheses () operator.

Live Code

<!DOCTYPE html><html lang="en"><body><script>

var addNumbersA = new Function('num1', 'num2', 'return num1 + num2');

console.log(addNumbersA(2, 2)); // logs 4

// could also be written the literal way, which is much more common
var addNumbersB = function(num1, num2) {return num1 + num2;};

console.log(addNumbersB(2, 2)); // logs 4

</script></body></html>

A function can be used to return a value, construct an object, or as a mechanism to simply run code. JavaScript has several uses for functions, but in its most basic form, a function is simply a unique scope of executable statements.

Function() Parameters

The Function() constructor takes an indefinite number of parameters, but the last parameter expected by the Function() constructor is a string containing statements that comprise the body of the function. Any parameters passed to the constructor before the last will be available to the function ...