Functional programming in Javascript

Functional Programming In JavaScriptFunctional Programming In JavaScript
Nikhil Kumar | Software Consultant
KnÓldus Software LLP
Nikhil Kumar | Software Consultant
KnÓldus Software LLP

AgendaAgenda
● Functional Programming : The Benefits
● Basic version Vs Filter
● Find
● Map
● Reduce
● Closures
● Now: var, let & const
● IIFE
All with comparisons

Functional programming is a paradigm which concentrates on
computing results rather than on performing actions. That is, when
you call a function, the only significant effect that the function has is
usually to compute a value and return it. Of course, behind the
scenes the function is using CPU time, allocating and writing memory,
but from the programmer's point of view, the primary effect is the
return value
Functional programming is a paradigm which concentrates on
computing results rather than on performing actions. That is, when
you call a function, the only significant effect that the function has is
usually to compute a value and return it. Of course, behind the
scenes the function is using CPU time, allocating and writing memory,
but from the programmer's point of view, the primary effect is the
return value
F P
Benefits of FP
 Less Bugs (less code)
 Easier to reason about
 Less Time
 Re-use more code.

FilterFilter
Filter is method on array objects that takes a function as a argument.
Filter expect its callback to return true or false.
var porche = cars.filter(function(carName){
return carName.brand === 'porche'
})

FindFind
works like as filter, but just return the first value.
var porche = cars.find(function(carName){
return carName.brand === 'porche'
})

MapMap
Map is function on the array object.
Map expect the callback function to return a transformed object,
Above 3 are used in – list transformation, they turn your list into something else.
var carList = []
for(var i = 0; i < cars.length; i++){
carList.push(cars[i].name)
}

ReduceReduce
Reduce is awesome, using reduce you can create functions like, map, find, filter or any other
list transformation. Reduce is super List Transformation tool, you can it to meet or your
requirements.
var priceSum = cars.reduce(function(sum, cars){
console.log("The sum of all cars", + sum, cars);
return sum + cars.price
},0);

ClosuresClosures
var myName = "nikhil"
function namesFun(){
console.log("Hey the name is " + myName);
}
namesFun();
Basically functions in javascript are closures actually, they can access the variables outside of
the functions, in languages that does not support closures we cannot do so.
Closure is a function inside a function.

Var is function scope let is block scope and don't talk about const
here.
Var is function scope let is block scope and don't talk about const
here.
Var => let => const
function count(){
for(var i = 0; i < 10; i++){
console.log(i);
}
}
count();
console.log(i);
//let
"use strict";
var i = 500;
for( i = 0; i< 101; i++){
console.log(i)
}
if(true){
/*let*/ i = 34000;
}
console.log(" show me ", i);

Using Let
let allows you to declare variables that are limited in scope to the block, statement, or
expression on which it is used. This is unlike the var keyword, which defines a variable
globally, or locally to an entire function regardless of block scope.
function varTest() {
var x = 1;
if (true) {
var x = 2; // same variable!
console.log(x); // 2
}
}
function letTest() {
let x = 1;
if (true) {
let x = 2; // different variable
}
}

Using Const
Constants are block-scoped, much like variables defined using the let statement. The value of
a constant cannot change through re-assignment, and it can't be redeclared.
The const declaration creates a read-only reference to a value. It does not mean the value
it holds is immutable, just that the variable identifier cannot be reassigned. For instance, in
case the content is an object, this means the object itself can still be altered.
"use strict";
const x= {
y: 10
}
//this can be done
x.y = 11;
//BUT
x = {
z:5;
}
console.log(x);

IIFE: Immediately Invoked Function Expression:IIFE: Immediately Invoked Function Expression:
(function(){
for(var i = 0; i < 10; i++){
console.log(i);
}
})();

References
Mozilla Documentation

Presenter
nikhil@knoldus.com
Presenter
nikhil@knoldus.com
Organizer
@Knolspeak
http://www.knoldus.com
http://blog.knoldus.com
Organizer
@Knolspeak
http://www.knoldus.com
http://blog.knoldus.com
Thanks

Functional programming in Javascript

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