5 / 2; // = 2.5

// Floor division

Math.floor(5/2); // =2

// Exponentiation

Math.pow(2,3); // =8

// There are three special not-a-real-number values:

Infinity; // result of e.g. 1/0

-Infinity; // result of e.g. -1/0

NaN; // result of e.g. 0/0, stands for 'Not a Number'

// Other data types

null; // deliberately assigned for a non-value initialization

undefined; // uninitialized value

// There's also a boolean type.

true;

false;

// parsing a numeral string

parseInt('123', 10); // 123

parseInt('010', 10); // 10

parseInt('11', 2); // 3

// Number.isNaN() to determine whether a given argument is a number or not

Number.isNaN('1'); // false

Number.isNaN(NaN); // true

//string operations

'hello'.length; // 5

'hello'.charAt(0); // "h"

'hello, world'.replace('world', 'mars'); // "hello, mars"

'hello'.toUpperCase(); // "HELLO"

// 0, empty strings (""), NaN, null, and undefined => false

// rest others => true

// declaring variables

let a; // = undefined

const a

'hello' + ' world'; // "hello world"

// from left to right if string is added to a number string concatenation is performed

'3' + 4 + 5; // "345"
3 + 4 + '5'; // "75"

// comparisons

123 == '123'; // true
1 == true; // true
123 === '123'; // false
1 === true; // false

for (let value of array) {
// do something with value
}

for (let property in object) {
// do something with object property
}

// Objects

// Type 1

let a = new Object(); // Object is defined in JS

// Type 2 (literal)

let a = {

name: "john fernandes",

id: 1234

}

// Example and usage

var obj = {
name: 'Carrot',
_for: 'Max', // 'for' is a reserved word, use '_for' instead.
details: {
color: 'orange',
size: 12
}
};

obj.details.color; // orange

obj['details']['size']; // 12

// Arrays

// Type 1

var a = new Array();
a[0] = 'dog';
a[1] = 'cat';
a[2] = 'hen';
a.length; // 3

// Type 2

var a = ['dog', 'cat', 'hen'];
a.length; // 3

// Looping through an array

for (var i = 0; i < a.length; i++) {
// Do something with a[i]
}

for (const currentValue of a) {
// Do something with currentValue
}

// Array methods

a.toString()

//Returns a string with the toString() of each element separated by commas.

a.join(sep)

//Converts the array to a string — with values delimited by the sep param

a.pop()

//Removes and returns the last item.

a.push(item1, ..., itemN)

//Appends items to the end of the array.

a.shift()

//Removes and returns the first item.

a.unshift(item1[, item2[, ...[, itemN]]])

//Prepends items to the start of the array.

a.slice(start[, end])

//Returns a sub-array.

a.sort([cmpfn])

//Takes an optional comparison function.

a.splice(start, delcount[, item1[, ...[, itemN]]])

//Lets you modify an array by deleting a section and replacing it with more items.

a.reverse()

//Reverses the array.

// Functions

function add(x, y) {
var total = x + y;
return total;
}

//functions have an inbuilt array of arguments

function add() {
var sum = 0;
for (var i = 0, j = arguments.length; i < j; i++) {
sum += arguments[i];
}
return sum;
}

add(2, 3, 4, 5); // 14

// more efficient way

function add(...args){

// do something with args array which can hold any number of arguments

}

// Anonymous function

var avg = function() {
var sum = 0;
for (var i = 0, j = arguments.length; i < j; i++) {
sum += arguments[i];
}
return sum / arguments.length;
};

// Creating class objects using constructor function notation

// note: this keyword

var s = makePerson('Simon', 'Willison');
s.fullName(); // "Simon Willison"
s.fullNameReversed(); // "Willison, Simon"

// exporting modules

// type 1 - conventional

// module.exports is an global object

function hello(){

//do something

}

module.exports = {

hello

}

// type 2 - ecma script for node versions >14

// using keyword exports

// refer blog https://www.freecodecamp.org/news/node-module-exports-explained-with-javascript-export-function-examples/

	Creado por Omkar Gan hace más de 5 años

Simple Nodejs tutorials