/* Declaring a variable means giving it a name. In JavaScript, this is often done with the let keyword. For example,
here is how you would declare a hello variable: */
let hello;
/* The console allows you to print and view JavaScript output. You can send information to the console using console.log().
For example, this code will print "Naomi" to the console: */
let developer = "Naomi";
console.log(developer);
/* When a variable is declared with the let keyword, you can reassign (or change the value of) that variable later on.
In this example, the value of programmer is changed from "Naomi" to "CamperChan".
Note that when reassigning a variable, you do not use the let keyword again.
*/
let programmer = "Naomi";
programmer = "CamperChan";
/*The default value of an uninitialized variable is undefined.
This is a special data type that represents a value that does not have a definition yet */
/* With the number data type, you can perform mathematical operations, like addition.
Try printing count + 1 to the console. */
let character = 'Hello';
let count = 8;
console.log(count+1);
/*Arrays are denoted using square brackets ([]). Here is an example of a variable with the value of an empty array: */
let array = [1, 3, 4];
/* You can make use of the .length property of an array
- this returns the number of elements in the array.
To get the last element of any array, you can use the following syntax: */
array[array.length - 1]
/* A method in JavaScript is a function that's associated with certain values or objects.
An example you've already encountered is the .log() method, which is part of the console object.
Arrays have their own methods, and the first you will explore is the .push() method.
This allows you to "push" a value to the end of an array. Here is an example to add the number 12 to the end of an array:*/
array.push(12);
console.log(array);
/* First, a const variable cannot be reassigned like a let variable. This code would throw an error:
const firstName = "Naomi";
firstName = "Jessica";
A const variable also cannot be uninitialized. This code would throw an error: */
/* You are going to start with a basic for loop. for loops use the following syntax:
for (iterator; condition; iteration) {
logic;
} */
/* a for...of loop, which iterates over each item in an iterable object and temporarily assigns it to a variable.
The syntax for a for...of loop looks like:
for (const value of iterable) {
}*/
/* Instead, you need to use the special escape sequence \n,
which is interpreted as a new line when the string is logged. For example:
lineOne = lineOne + "\n" + lineTwo; */
/* o achieve this, you will use the .repeat() method available to strings.
This method accepts a number as an argument, specifying the number of times to repeat the target string. For example, using .repeat() to generate the string "Code! Code! Code!":
const activity = "Code! ";
activity.repeat(3); */
/* A function is a block of code that can be reused throughout your application.
Functions are declared with the following syntax:
function name(parameter) {
}
The function keyword tells JavaScript that the name variable is going to be a function.
parameter is a variable that represents a value that is passed into the function when it is used.
A function may have as many, or as few, parameters as you'd like.
Like a for loop, the space between the curly braces is the function body.
The syntax for a function call is the function name followed by parentheses
In order to return something else, you need to use the return keyword.
Here is an example of a function that returns the string "Functions are cool!":
function demo() {
return "Functions are cool!";
}*/
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Javascript(JS) is a object-oriented programming language which adhere to ECMA Script Standards. Javascript is required to design the behaviour of the web pages.
var readline = require('readline');
var rl = readline.createInterface({
input: process.stdin,
output: process.stdout,
terminal: false
});
rl.on('line', function(line){
console.log("Hello, " + line);
});
| Keyword | Description | Scope |
|---|---|---|
| var | Var is used to declare variables(old way of declaring variables) | Function or global scope |
| let | let is also used to declare variables(new way) | Global or block Scope |
| const | const is used to declare const values. Once the value is assigned, it can not be modified | Global or block Scope |
let greetings = `Hello ${name}`
const msg = `
hello
world!
`
An array is a collection of items or values.
let arrayName = [value1, value2,..etc];
// or
let arrayName = new Array("value1","value2",..etc);
let mobiles = ["iPhone", "Samsung", "Pixel"];
// accessing an array
console.log(mobiles[0]);
// changing an array element
mobiles[3] = "Nokia";
Arrow Functions helps developers to write code in concise way, it’s introduced in ES6.
Arrow functions can be written in multiple ways. Below are couple of ways to use arrow function but it can be written in many other ways as well.
() => expression
const numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
const squaresOfEvenNumbers = numbers.filter(ele => ele % 2 == 0)
.map(ele => ele ** 2);
console.log(squaresOfEvenNumbers);
let [firstName, lastName] = ['Foo', 'Bar']
let {firstName, lastName} = {
firstName: 'Foo',
lastName: 'Bar'
}
const {
title,
firstName,
lastName,
...rest
} = record;
//Object spread
const post = {
...options,
type: "new"
}
//array spread
const users = [
...adminUsers,
...normalUsers
]
function greetings({ name = 'Foo' } = {}) { //Defaulting name to Foo
console.log(`Hello ${name}!`);
}
greet() // Hello Foo
greet({ name: 'Bar' }) // Hi Bar
IF is used to execute a block of code based on a condition.
if(condition){
// code
}
Else part is used to execute the block of code when the condition fails.
if(condition){
// code
} else {
// code
}
Switch is used to replace nested If-Else statements.
switch(condition){
case 'value1' :
//code
[break;]
case 'value2' :
//code
[break;]
.......
default :
//code
[break;]
}
For loop is used to iterate a set of statements based on a condition.
for(Initialization; Condition; Increment/decrement){
//code
}
While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.
while (condition) {
// code
}
Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.
do {
// code
} while (condition);
ES6 introduced classes along with OOPS concepts in JS. Class is similar to a function which you can think like kind of template which will get called when ever you initialize class.
class className {
constructor() { ... } //Mandatory Class method
method1() { ... }
method2() { ... }
...
}
class Mobile {
constructor(model) {
this.name = model;
}
}
mbl = new Mobile("iPhone");