Object Handling in JavaScript

Declaration and Update

Object Declaration

• Using object literal: {}
• Using constructor: new Object()

Accessing Values

• Dot notation: object.key
• Bracket notation: object["key"]

Check if a Key Exists

• Using hasOwnProperty: object.hasOwnProperty("key")
• By retrieving the value: if (object.key !== undefined)

Delete a Property

• delete object.key

Iterating Through an Object

• Using for...in loop:

  for (let key in object) {
    if (object.hasOwnProperty(key)) {
      console.log(key, object[key]);
    }
  }

---

Object Methods

Object.keys()

• Description: Returns all enumerable keys of the given object (excludes Symbol keys).
• Example:

  Object.keys({ a: 1, b: 2 }); // ["a", "b"]

Object.values()

• Description: Returns all enumerable values of the given object (excludes Symbol keys).
• Example:

  Object.values({ a: 1, b: 2 }); // [1, 2]

Object.assign()

• Description: Copies the properties of one or more source objects to a target object.
• Example:

  let target = { a: 1 };
  let source = { b: 2 };
  Object.assign(target, source); // { a: 1, b: 2 }

Spread Operator

• Description: Concatenates objects without mutating the original objects.
• Example:

  let obj1 = { a: 1 };
  let obj2 = { b: 2 };
  let combined = { ...obj1, ...obj2 }; // { a: 1, b: 2 }

Object.create()

• Description: Creates a new object with a specified prototype.
• Example:

  let proto = { a: 1 };
  let obj = Object.create(proto); // obj inherits properties from proto

Object.defineProperty()

• Description: Defines a property with specific descriptors (e.g., writable, enumerable, configurable).
• Example:

  Object.defineProperty(obj, "key", {
    value: 10,
    writable: false,
    enumerable: true,
    configurable: false,
    get() {
      return key;
    },
    set(val) {
      key = val;
    },
  });
  Refer: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty

Object.defineProperties()

• Description: Defines multiple properties with descriptors.
• Example:

  Object.defineProperties(obj, {
    key1: { value: 10, writable: true },
    key2: { value: 20, enumerable: false },
  });

Object.propertyIsEnumerable()

• Description: Checks if a property is enumerable.
• Example:

  obj.propertyIsEnumerable("key"); // true/false

Object.entries()

• Description: Converts an object into an array of key-value pairs.
• Example:

  Object.entries({ a: 1, b: 2 }); // [["a", 1], ["b", 2]]

Object.fromEntries()

• Description: Converts an array of key-value pairs into an object.
• Example:

  Object.fromEntries([
    ["a", 1],
    ["b", 2],
  ]); // { a: 1, b: 2 }

Object.freeze()

• Description: Freezes an object, making it immutable.
• Example:

  Object.freeze(obj);

Object.isFrozen()

• Description: Checks if an object is frozen.
• Example:

  Object.isFrozen(obj); // true/false

Object.preventExtensions()

• Description: Prevents new properties from being added to an object.
• Example:

  Object.preventExtensions(obj);

Object.isExtensible()

• Description: Checks if an object is extensible.
• Example:

  Object.isExtensible(obj); // true/false

Object.seal()

• Description: Seals an object, preventing new properties and making existing properties non-configurable.
• Example:

  Object.seal(obj);

Object.isSealed()

• Description: Checks if an object is sealed.
• Example:

  Object.isSealed(obj); // true/false

Object.getOwnPropertyDescriptor()

• Description: Returns the descriptor of a specific property.
• Example:

  Object.getOwnPropertyDescriptor(obj, "key");

Object.getOwnPropertyDescriptors()

• Description: Returns descriptors of all properties.
• Example:

  Object.getOwnPropertyDescriptors(obj);

Object.getOwnPropertyNames()

• Description: Returns an array of all property names (including non-enumerable properties).
• Example:

  Object.getOwnPropertyNames(obj);

Object.getOwnPropertySymbols()

• Description: Returns only symbol keys of an object.
• Example:

  Object.getOwnPropertySymbols(obj);

Object.getPrototypeOf()

• Description: Returns the prototype of an object.
• Example:

  Object.getPrototypeOf(obj);

Object.is()

• Description: Compares two objects. Returns true only if they are the same instance.
• Example:

  Object.is(obj1, obj2); // true/false

Object.setPrototypeOf()

• Description: Sets the prototype of an object. (Note: Avoid this for performance reasons.)
• Example:

  Object.setPrototypeOf(obj, proto);