JavaScript Revision Part 01

How to print output on the screen

We use console.log(" ") to print anything in JavaScript To print the value of a variable we use`as a console. log(This is a ${variable}`)

How to give user input in JavaScript

We use prompt()

How to add Comments in JavaScript

// single line, /**/ multiple line comment

Variables:

They are placeholders used to store information There are 3 types of variables in JavaScript var let const let and const are present in the temporal dead zone become active only when they are initialized var is hoisted and the initial value is undefined.

Data Types

Types of Data Types in JavaScript

1. Primitive

2. Objects

3. Primitive: a.number (of any kind whether it is decimal, float) b.string (a string of any type) c.boolean ( true or false) d. Big Int e.Symbol() ---Introduced in ES6

4. objects Which store collection of elements array -represented by array[] objects- represented by {}

Introduced in ES6 3.Map It is like an object but the only difference is it is iterable and ordered

4.Set It will only have unique values

Mathematical Operators

• add
• subtract / divide % modulo gives the remainder ** exponent

Math Methods

Math.floor() Rounds up Math.ceil() rounds down

Type conversion and coercion

Type Conversion is explicitly converting the type of data into another the type of() function can be used to check the type of the variable Example: Number(), String()

Type coercion happens when an operator deals with 2 values of different data types. Behind the scenes, JavaScript automatically converts one data type to match the other so the operation can be executed.

Conditional Operator result is true or false

1.Difference between == and === == will check if the value is equal or not irrespective of the data type === will check for both the values as well as the data type also called as strict equality use this always < less than

greater than != this will perform type coercion and will check for value only !== will check for both types as well the value also called as strict!== use this always

Logical Operator

||-or &&-and !-not

Truth and Falsy Values

Falsy Values are false 0 (zero) -0 (minus zero) 0n (BigInt zero) '', "", `` (empty string) null undefined NaN

Everything else is truth

Increment and Decrement operator

a++,a-- ++a,--a

Ternary Operator

condition?if condition is true evaluate this : if condition is false evaluate this part

Conditional Statements

Single if statement if(condition is true){ evaluate }

If else ladder

if(condition true){ evaluate ;} else{ evaluate when if the condition is false }

Switch Statement

switch(variable){ case 1: Perform break default: perform }

if no break written program will free flow from case matched till end in case we should get a value

Loops

while(condition){ evaluate till the condition is false }

for(let i=0;i<value;i++{ evaluate till i is less than the value }

do { will always execute once then will execute only if the condition in the while is true }while(condition)

null vs undefined

null means that value does not exist (here we are implying that the value is defined by its null) undefined means values have not been initialized, by default everything in JavaScript has this state until defined

Exception Handling

try{ // all the code written in this line will be executed until we get an error

} catch(error){ // the moment we get an error code in this block will be executed. }

Block In JavaScript

Anything written inside curly braces is block scoped Example: { // this is block scoped }