If else :

In js the else part doesn't take any condition but there will be no error if you put condition in else part, but it can result to uneven results:

// let a= prompt("u r age : ")     // to enter a value
// console.log(typeof a)       // used to know the datatype of a
// a = Number.parseInt(a)     // used to convert data type to number
// console.log(typeof a)
// if(a>0)
// {
//   console.log("valid age")
// }
// else
// {
//   console.log("not valid")
// }

//
//      else case with condition
let a ="hii"
if( a== "he")
{
  console.log("he")
}
else if( a== "she")
{
  console.log("she")
}
else if( a== "hii")
{
  console.log("hii")
}
else( a== "me")
{
  console.log("me")
}

switch case: It is a selection control statement.

let n = "gkd";
switch (n) {
  case "hd":
    console.log("himanshu");
    break;
  case "gkd":
    console.log("gopal");
    break;
  default:
    console.log("nothing");
}

For loop:

for(let i=0 ; i<=5;i++)
  {
    console.log(i)
  }

//                     program to add number
let sum = 0
let n= prompt('enter any no : ')
n =Number.parseInt(n);  // here you have ability to skip this conversion but it
//is necessary to change it as n is a string by default here and hence can lead 
// to the unrequired results
for(let i=0;i<=n;i++)
  {
    sum += i
  }
console.log("the sum is ")
console.log(sum)

While loop:

  // let n = prompt("enter number ")
  // //n = Number.parseInt(n)
  // let i =0
  // while(i<=n)
  //   {
  //     console.log(i)
  //     i++
  //    }

dowhile loop:

 let a = 3;
  do{
    console.log("hii")
  }while(a>5)

ternary operator:

 // let age = prompt("enetr age")
  // age = Number.parseInt(age)

  // // console.log(age>18?'valid age':'invalid age')

  // // or

  // age>18?console.log("can vote"):console.log("cant vote")

lt.31link: https://hashnode.com/post/cltenwn7m00020al78z6p0zma