The Object.keys() static method returns an array of a given object's own enumerable string-keyed property names.
Syntax
Object.keys(obj)
Parameters
obj- : An object.
Return value
An array of strings representing the given object's own enumerable string-keyed property keys.
Description
Object.keys() returns an array whose elements are strings corresponding to the enumerable string-keyed property names found directly upon object. This is the same as iterating with a for...in loop, except that a for...in loop enumerates properties in the prototype chain as well. The order of the array returned by Object.keys() is the same as that provided by a for...in loop.
If you need the property values, use Object.values instead. If you need both the property keys and values, use Object.entries instead.
Examples
Using Object.keys()
// Simple array
const arr = ["a", "b", "c"];
console.log(Object.keys(arr)); // ['0', '1', '2']
// Array-like object
const obj = { 0: "a", 1: "b", 2: "c" };
console.log(Object.keys(obj)); // ['0', '1', '2']
// Array-like object with random key ordering
const anObj = { 100: "a", 2: "b", 7: "c" };
console.log(Object.keys(anObj)); // ['2', '7', '100']
// getFoo is a non-enumerable property
const myObj = Object.create(
{},
{
getFoo: {
value() {
return this.foo;
},
},
},
);
myObj.foo = 1;
console.log(Object.keys(myObj)); // ['foo']
If you want all string-keyed own properties, including non-enumerable ones, see Object.getOwnPropertyNames.
Using Object.keys() on primitives
Non-object arguments are coerced to objects. Only strings may have own enumerable properties, while all other primitives return an empty array.
// Strings have indices as enumerable own properties
console.log(Object.keys("foo")); // ['0', '1', '2']
// Other primitives have no own properties
console.log(Object.keys(100)); // []
Note: In ES5, passing a non-object to
Object.keys()threw a TypeError.