JavaScript Object.keys()

let Student = {
  name: "Lisa",
  age: 24,
  marks: 78.9,
};

// get all keys of Student
let std1 = Object.keys(Student);
console.log(std1);

// Output: [ 'name', 'age', 'marks' ]

keys() Syntax

The syntax of the keys() method is:

Object.keys(obj)

The keys() method, being a static method, is called using the Object class name.

keys() Parameters

The keys() method takes in:

• obj - the object whose enumerable properties are to be returned.

keys() Return Value

The keys() method returns an array of strings that represent all the enumerable properties of the given object.

Note: The ordering of the properties is the same as that when looping over them manually.

Example: Using Object.keys()

// Array objects
const arr = ["A", "B", "C"];
console.log(Object.keys(arr)); // ['0', '1', '2']

// array-like objects
const obj = { 65: "A", 66: "B", 67: "C" };
console.log(Object.keys(obj)); // ['65', '66', '67']

// random key ordering
const obj1 = { 42: "a", 22: "b", 71: "c" };
console.log(Object.keys(obj1)); // ['22', '42', '71']

// string => from ES2015+, non objects are coerced to object
const string = "code";
console.log(Object.keys(string)); // [ '0', '1', '2', '3' ]

Output

[ '0', '1', '2' ]
[ '65', '66', '67' ]
[ '22', '42', '71' ]
[ '0', '1', '2', '3' ]

Recommended Reading:

• Javascript Object entries()