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Object

Object.keys, values, entries

Methods Description
Object.keys(obj) Returns an array of keys.
Object.values(obj) Returns an array of values.
Object.entries(obj) Returns an array of [key, value] pairs.

Iterate Object

Methods Description
for key in object iterates over an object
for [key, value] of Object.entries(obj) iterates iterable value (Array, String) 
let user = {
  name: "John",
  age: 30,
};

console.log(Object.keys(user));
//[ 'name', 'age' ]

console.log(Object.values(user));
// [ 'John', 30 ]

console.log(Object.entries(user));
//[ [ 'name', 'John' ], [ 'age', 30 ] ]

for (key in user) {
  console.log(`${key}, ${user[key]}`);
}
// name, John
// age, 30

for ([key, value] of Object.entries(user)) {
  console.log(`${key}, ${value}`);
}
// name, John
// age, 30

for...of

Syntax

for (variable of iterable) {
  statement;
}

Iterating over an Array

const iterable = [10, 20, 30];

for (const value of iterable) {
  console.log(value);
}
// 10
// 20
// 30

Iterating overf a String

const iterable = "boo";

for (const value of iterable) {
  console.log(value);
}
// "b"
// "o"
// "o