What's the difference between a method and a function?

Question

Can someone provide a simple explanation of methods vs. functions in OOP context?

Answer 1

Here is some explanation for method vs. function using JavaScript examples:

test(20, 50); is function define and use to run some steps or return something back that can be stored/used somewhere.

You can reuse code: Define the code once and use it many times.

You can use the same code many times with different arguments, to produce different results.

var x = myFunction(4, 3);   // Function is called, return value will end up in x

function myFunction(a, b) {
    return a * b;          // Function returns the product of a and b
}

var test = something.test(); here test() can be a method of some object or custom defined a prototype for inbuilt objects, here is more explanation:

JavaScript methods are the actions that can be performed on objects.

A JavaScript method is a property containing a function definition.

Built-in property/method for strings in javascript:

var message = "Hello world!";
var x = message.toUpperCase();
//Output: HELLO WORLD!

Custom example:

function person(firstName, lastName, age, eyeColor) {
    this.firstName = firstName;  
    this.lastName = lastName;
    this.age = age;
    this.eyeColor = eyeColor;
    this.changeName = function (name) {
        this.lastName = name;
    };
}

something.changeName("SomeName"); //This will change 'something' objject's name to 'SomeName'

You can define properties for String, Array, etc as well for example

String.prototype.distance = function (char) {
    var index = this.indexOf(char);

    if (index === -1) {
        console.log(char + " does not appear in " + this);
    } else {
        console.log(char + " is " + (this.length - index) + " characters from the end of the string!");
    }
};

var something = "ThisIsSomeString"

// now use distance like this, run and check console log

something.distance("m");

Some references: Javascript Object Method, Functions, More info on prototype