Object.keys()

const object = {
  a: "some string",
  b: 42,
  c: false,
};

console.log(Object.keys(object));
// : Array ["a", "b", "c"]

Object.keys(obj)

// 
const arr = ["a", "b", "c"];
console.log(Object.keys(arr)); // ['0', '1', '2']

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

// 
const anObj = { 100: "a", 2: "b", 7: "c" };
console.log(Object.keys(anObj)); // ['2', '7', '100']

// getFoo 
const myObj = Object.create(
  {},
  {
    getFoo: {
      value() {
        return this.foo;
      },
    },
  },
);
myObj.foo = 1;
console.log(Object.keys(myObj)); // ['foo']

// 
console.log(Object.keys("foo")); // ['0', '1', '2']

// undefined  null 
console.log(Object.keys(100)); // []