Arrays, Objects and Classes

Array Methods

Method	Does	Mutates?
push / pop	Add / remove at end	Yes
unshift / shift	Add / remove at start	Yes
splice	Insert / remove anywhere	Yes
slice	Copy a portion	No
map / filter / reduce	Transform / select / combine	No
find / includes / indexOf	Search	No
sort	Sort (as strings by default!)	Yes

JavaScript

console.log([10, 9, 1, 100].sort());
console.log([10, 9, 1, 100].sort((a, b) => a - b));

[ 1, 10, 100, 9 ] [ 1, 9, 10, 100 ]

Objects, Destructuring and Spread

JavaScript

const student = { name: "Meera", roll: 12, branch: "CSE" };
const { name, ...rest } = student;           // destructuring
const updated = { ...student, roll: 15 };    // spread copy
console.log(name, rest);
console.log(updated);
console.log(Object.keys(student), JSON.stringify(student));

Meera { roll: 12, branch: 'CSE' } { name: 'Meera', roll: 15, branch: 'CSE' } [ 'name', 'roll', 'branch' ] {"name":"Meera","roll":12,"branch":"CSE"}

Classes

JavaScript

class Animal {
    #sound;                                  // private field
    constructor(name, sound) { this.name = name; this.#sound = sound; }
    speak() { return this.name + " says " + this.#sound; }
}
class Dog extends Animal {
    constructor(name) { super(name, "woof"); }
    fetch() { return this.name + " fetches the ball"; }
}
const d = new Dog("Bruno");
console.log(d.speak());
console.log(d.fetch());

Bruno says woof Bruno fetches the ball

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