notes

In JavaScript, slice() is used to extract a portion of an array or string without modifying the original. It works on arrays and strings. It does not modifies original.

array.slice(start, end); string.slice(start,end) 

In JavaScript, any non promitive data type is a kind of object hence ,arrays are a special kind of object, which is why - [1,3] is // "object"

In JavaScript, the for...of loop is used to iterate over the values of an iterable object, such as an array, string, Map, or Set. It gives you direct access to each element’s value, making it ideal when you only care about the data itself. On the other hand, the for...in loop is used to iterate over the keys (or property names) of an object. It’s commonly used for looping through object properties rather than array elements. While for...in works with objects and returns the keys as strings, for...of works with iterables and returns their actual values. Therefore, for...of is better suited for arrays and other iterable structures, while for...in is typically used for plain JavaScript objects.

const arr = ["a", "b", "c"];
for (const x of arr) console.log(x); // a, b, c
for (const x in arr) console.log(x); // 0, 1, 2
// in → key , use of in should be avoided for arrays 
// of → value

const fruits = ["apple", "banana", "mango"];
console.log(fruits.includes("banana")); // true
console.log(fruits.includes("ban"));  // false , full element should match
console.log(fruits.shift()); //	Removes the first element of an array, and returns that element
console.log(fruits.unshift()); // Adds new elements to the beginning of an array, and returns the new length
console.log(fruits.push("orange")); // push() → Add element at the END
console.log(fruits.pop());  // Returns removed element -> "orange"

"hello world".split() // No separator is provided ,The entire string becomes one single array element. // ["hello world"]
"hello world".split("") // Empty string "" is used as the separator,The string is split character by character // ["h","e","l","l","o"," ","w","o","r","l","d"]

["h", "e", "l", "l", "o"].join() // JavaScript uses comma , as the default separator . output -"h,e,l,l,o"
["h", "e", "l", "l", "o"].join("") // Elements are joined without anything in between . output - "hello"
// to reverse a string 
let reversed = str.split("").reverse().join("");

we can also use js object as map.but objects only accept string or symbol keys — not other data types.

const map = new Map();
// Add key-value pairs
map.set('name', 'Harmeet');
map.set('age', 25);
map.set(true, 'Yes'); // can use boolean as key

// Get a value
console.log(map.get('name')); // "Harmeet"

// Check if key exists
console.log(map.has('age')); // true

// Delete a key
map.delete('age');

// Get map size
console.log(map.size); // 2

// Iterate through entries
for (const [key, value] of map) {
  console.log(key, value);
}


 The structuredClone() method in JavaScript is a built-in global function used to create a deep copy of an object or value.

string 

string - js 

// string matching js
const text = "JavaScript is fun";
console.log(text.includes("Script")); // true
console.log(text.includes("script")); // false (case-sensitive)
let s2 = 'World';
let s3 = `Hello ${s2}`; // template literal

// string matching python
string - pyton 
text = "Python is awesome"
print("Python" in text)     # ✅ True
print("python" in text)     # ❌ False (case-sensitive)


js code snippets 
To find quotient use 

let quotient = Math.floor(sum / 10); // sum/10  would give a float value is it is not fully divisible 

different naming conventions
naming conventions — 
ways to write multi-word names (like variables, functions, classes) in code


  

    

      
Style
      
Example
      
Common Use Case
    
  
  

    

      
camelCase
      
userName
      
JS variables, functions, object keys
    
    

      
PascalCase
      
UserName
      
Classes, React components
    
    

      
snake_case
      
user_name
      
Python, databases, environment variables
    
    

      
kebab-case
      
user-name
      
CSS class names, HTML attributes