Object.keys()

const object1 = {
  a: "somestring",
  b: 42,
  c: false,
};

console.log(Object.keys(object1));
// Expected output: 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)); // []