Var Rules, Loops,String

Variable Rules

1. Can start with underscore or letters or a $ symbol only
2. Can contain symbols,letts,and number
3. Reserved words cannot be used as variables
4. Javascript is case sensitive

REPL

R

Read

E

Evaluate

P

Print

L

Loop

Loops

  
  const obj={
    name:"warlord",
    age:"99"
  };
  for(const i in obj){ // "for in" is used for objects that show values in form of dictionaries
  const val=obj[i]
  console.log(i,val)
  }
  for(const i of obj.name){// "for of" is usually used for strings - arrays / iterables
  console.log(i)
  }
  
  

  
  object.forEach((value,index,object)=>
  console.log(value,index,object);
  })
  
  

Sample Function

Function Statement [declaration]

Can be hoisted

Function Expression [assigning the return value to a variable]

• Assigned to a variable
• Can be anonymous

Arrow Function

• Shorter syntax
• cannot use
  1. this
  2. super
  3. new.target [ to check wether a target was called using new]

IIFE

• Creates a private scope
• Avoids polluting the global scope

ES

Parameters

  
  function makeLunch(opts){
  const {main,side,drinks}=opts // naming those parameters
  }
  makeLunch({main:"🍞",side:"🥭",drinks:"🍷"}) // passing those arguments
  
  

  
function makeLunch(...args){

}
makeLunch('🍇','🍈','🍉','🍊','🍌','🍍')
  
  

  
  const makeWine=(qty)=>{
   return '🍷'.repeat(qty);
  }
  
  

  
  const makeWine=(qty)=> '🍷'.repeat(qty)
  
  

  
let x=2;
const impure =() =>{
x++;
return x**2;
}
const pure =(x) =>{
x++;
return x**2;
}
  
  

let haveFun=()=>console.log("Having Fun");
setTimeout(haveFun,500);
  

  

function tell(name,time){
console.log(`hello ${name}`)
console.log(`hope master [${name}] is doing well!`)
console.log(`its ${time} right now`)
}

const now=new Date();

const curtime=`${now.getHours()}:${now.getMinutes()}:${now.getSeconds()}`;

tell("warlord",curtime)
  
  

Strings

  
let a="warlord"
console.log(a);
console.log(a[0]);
console.log(a[1]);
console.log(a[2]);
console.log(a[3]);
console.log(a[4]);
console.log(a[5]);
console.log(a[6]);

console.log(a.length); // 7
console.log(a.toUpperCase()); // WARLORD
console.log(a.toLowerCase()); // warlord
console.log(a.slice(1,5)); // prints from 1 to 5 - arlor
console.log(a.slice(3)); // prints from 3 to end - lord
console.log(a.replace("war","speed")); // speedlord
console.log(a.concat("088")); //warlord088
console.log(a.charAt(3)); // l
console.log(a.indexOf("war")) // 0
console.log(a); // warlord

// refer 'primitives' under 'basics' to know about `shift` and `unshift` string method - shift - pop from start , unshift - push in the start




let number=[1,2,3,4,5]
console.log(number.splice(1,3));  // 2,3,4 are REMOVED - now number=[1,5]
console.log(number.splice(1,3,222,333)); // 2,3,4 are removed and specified number [222,333] are ADDED

// SLICE doesn't modify the original array - just works on the shallow copy . 
// used for copying without changes

// SPLICE modified the original array - can remove replace and add elements .
// used for editing in place


console.log(number)// [ 1 , 2 , 3 , 4 , 5 ]
console.log(number.toString()) // 1,2,3,4,5 -- again prints a shallow copy
// if you want to convert back to array in order to perform function like - MAP FILTER REDUCE 
// do number =  number.split(",")
console.log(Array.from(number))
console.log(number.join(" and ")) // 1 and 2 and 3 and 4 and 5

let b="flashbang";
console.log(a+" uses "+b);
//or 
console.log(`${a} used ${b}`);
// we can also have stuff like double quotes in side the backticks like -- 

console.log(`"${a}" uses "${b}"`);

console.log("\""+a+"\" uses \""+b+"\"");
  
  

Map-Filter-Reduce

Code for Map

let arr=[1,2,3,4,5]
let newarr=arr.map((e,value,array)=>{ // value and array are not necessary here 
return e**2 
})
console.log(newarr)
// could also be written in short hand like - 
let newArr=arr.map(e=>{
return e**2;
})
  

Code for Filter

let arr=[1,2,3,4,5]
let newarr=arr.map(e=>{
return e**2
})
console.log(newarr)
const greaterThanSeven = (e)=>{
if(e>7){
return true
}
return false
}
newarr.filter(greaterThanSeven)
  

Code for reduce

  
let arr=[1,2,3,4,5,6]
const red=(a,b)=>{
return a*b;
}
console.log(arr.reduce(red))