Functions are defined, or declared, with the function keyword. A factory function is any function which is not a class or constructor that returns a (presumably new) object. (It is possible to attach a new function to a instance in JavaScript). function is the keyword that starts declaring a function. Defining a Function. In your first statement the constructor function called is an already defined function, Function . There’s a lot going on in the example above, so let’s look at each part individually. In this tutorial, we will learn several ways to define a function, call a function, and use function parameters in JavaScript. A JavaScript Function is a JavaScript Variable until it is executed (evaluated). Let’s see an example: ; The read() method should use prompt to read a new number and add it to value. One more thing: new Function. If it does not find there then it uses studObj's __proto__ link which points to the prototype object of Student function. You can add functions to this prototype property, and in this form, it is known as a method. Normally, it is better to use new Function() than eval() to evaluate code: The function parameters provide a clear interface to the evaluated code and you don’t need the slightly awkward syntax of indirect eval() in order to ensure that the evaluated code can only access its own and global variables. A function object includes a string which holds the actual code -- the function body -- of the function. It works like creating a new function, but as functions are objects in JavaScript, you create an object. When an inherited function is executed, the value of this points to the inheriting object. JavaScript functions are a special type of objects, called function objects. The following code uses the createPerson() factory function to create two objects john and jane: In JavaScript, any function can return an object. Before we use a function, we need to define it. The code is literally just a string. This section explains how to write your own functions in JavaScript. Note, that when a function is called with the new keyword in javascript it exhibits special behavior. Below is the syntax for a function in JavaScript. JavaScript allows us to write our own functions as well. ; addTwoNumbers is the function’s name, which is customizable — just like variable names. function nameOfFunction() { // Code to be executed } Code language: JavaScript (javascript) When a function creates an object, it is called a factory function. Create a constructor function Accumulator(startingValue).. Function Definition. (x, y) are parameters, variable names for the inputs a function will accept. The createPerson() is a factory function because it returns a new person object. Object that it creates should: Store the “current value” in the property value.The starting value is set to the argument of the constructor startingValue. Read on for a full explanation. 6. In JavaScript functions are first-class objects - a function is a regular object of type function. Every JavaScript function has a prototype property, which is empty by default. When an object is created using the constructor, it inherits all its properties and methods: Example Copy The ways of the declaration described above create the same function object type.