Functional Programming in JS

Functions

Function Statement / Function Declaration

This way of creating a function is called Function Statement.

function statement() {
  console.log("I'm a Function Statement.");
}

Function Expression

Assigning a function to a variable is called Function Expression.

var expression = function () {
  console.log("I'm a Function Expression.");
};

Difference between Function Statement and Function Expression

• The difference is hoisting.
• We can call the Function Statement before declaring it.
• But, Doing that in Function Expression will throw an Error. Coz, We called it before creating the function.
• Function Expressions are treated the same as Variables.

Anonymous Functions.

• They dont have their own identity.
• function () { } -> Will throw an Error stating "Function statements require a function name".
• Can be used in Function Expressions and Closures Etc.,

Uses of Anonymous Functions:

• When function are used as values. i.e., Function Expressions.
• Callback Functions. Which are passed as an Argument in other Functions.
• Immediately Invoked Function Expressions (IIFE). Eg:

(function () {
  console.log("I will run immidiately");
})();

• Event Handlers. Eg:

.addEventListener("click", function() {
    alert("Button clicked!")
    });

• Higher Order Functions.
• Creating Closures.

Named Function Expression.

• A named function expression allows you to define a function with a name that is only accessible within the function itself.
• Unlike regular Functions, Named Functions are not hoisted and only accessible within scope.
• Eg:

const fun = function namedFn() {
  console.log("I'm a named function");
};

Diff. between Parameters & Arguments

function hi(greet, name) {
  // greet and name are paramenters.
  console.log(greet + "! " + name);
}
hi("Hi", "Siddhiq"); // The values passed to the Function's Parameters are Arguments.

First-Class Functions.

• First Class Functions are the First Class Citizens. Meaning that they enjoy all the rights and privileges of any other variable or object in the language.
• First Class Functions can be passed as Arguments, Returned, and Stored as Variables.
• They are treated as Objects.