Mastering JavaScript Fundamentals: A Starter's Handbook

for..in v/s for...of:

By using the for..in i get the indexes only but with the help of those indexes i can get the values at that index.

By using the for...of I can only get the value only values directly I don’t get the indexes.

    <script>
 let arr=["apple","banana","guava"];
for(i in arr){
document.writeln(`index=${i}`);
document.writeln(`value=${arr[i]});
}
for(i of arr)
{
document.writeln('value=${i}`);
}
   </script>

Here we can observe the differences easily

for of vs for Each()

for of will works for Arrays, strings, maps, sets but for each will works Arrays only .

foreach always need the callback function

Functions in JavaScript

Function with parameter and return type.

Function with default Parameter

function greet(name="alice")
{
document.writeln(" Hii "+ name);
}
greet();// Hii alice
greet("Vaishu"); // Hii vaishu

let’s discuss arrow functions in detail

Arrow Functions

Arrow function is shorter way to write a function in JavaScript

it uses the => symbol instead of function keyword.

Callback Function

It is simply a function that is passed as argument to another function

callback adds the extra functionality to function and control the order of execution

<script>

    function before(c)
    {
        for(let k=0;k<10;k++){
        console.log(k)
        c(k);
        }
    }
    function c(n)
    {
        console.log(` number ${n}`)
    }
    before(c)

</script>

What is splice and slice in JavaScript^🤔

Slice()

Extracts a portion of array or string without modifying the original

syntax

array. slice(start, end);

here the end is not included

splice()

changes the original array by removing, adding, replacing.

array. splice(start,deletecount,item1,item2…);