`Object.entries`

Returns an array of given object’s own enumerable string-keyed property key-value pairs in a tuple-like array

// object literal
const obj = { foo: "bar", baz: 42 };
Object.entries(obj); // [['foo', 'bar'], ['baz', 42]]

// Array-like object
const obj = { 0: "a", 1: "b", 2: "c" };
console.log(Object.entries(obj)); // [['0', 'a'], ['1', 'b'], ['2', 'c']]

// Array-like object with random key ordering
const anObj = { 100: "a", 2: "b", 7: "c" };
Object.entries(anObj); // [['2', 'b'], ['7', 'c'], ['100', 'a']]

`Object.keys`

Returns an array of a given object’s own enumerable string-keyed property names. Works for array-like object.

// Simple array (returns index)
const arr = ["a", "b", "c"];
Object.keys(arr); // ['0', '1', '2']

// Array-like object
const obj = { 0: "a", 1: "b", 2: "c" };
Object.keys(obj); // ['0', '1', '2']

// Array-like object with random key ordering
const anObj = { 100: "a", 2: "b", 7: "c" };
Object.keys(anObj); // ['2', '7', '100']

Usage on primitives

// Strings have indices as enumerable own properties
Object.keys("foo"); // ['0', '1', '2']

// Other primitives have no own properties
Object.keys(100); // []

`Object.freeze()`

What is it

Static method that freezes an object

Freezing an object prevents extensions and makes existing properties non-writable and non-configurable

A frozen object can no longer be changed:

new properties cannot be added
existing properties cannot be removed
their enumerability, configurability, writability, or value cannot be changed
the object's prototype cannot be re-assigned

freeze() returns the same object that was passed in

const obj = {
  prop: 42,
};

Object.freeze(obj);

// Throws an error in strict mode
obj.prop = 33;

`Object.freeze` vs `as const`

Object.freeze is a runtime method whereas as const is compile time method

as const makes plain object not be able to be modified

const plainObject = {
  name: "josh",
  number: 1,
  status: "offline",
} as const

Typing Object Destructuring

const obj = { a: 5, b: 7, c: 9 };

// Object.entries()
Object.entries(obj).map(([key, value]) => {
  console.log(key); // a, b, c
  console.log(value); // 5, 7, 9
})

// for...of
for(const [key, value] of Object.entries(obj)) {
  console.log(`${key} ${value}`); // "a 5", "b 7", "c 9"
}

// using forEach
Object.entries(obj).forEach(([key, value]) => {
  console.log(`${key} ${value}`); // "a 5", "b 7", "c 9"
});

Object Methods

Object.entries

Object.keys