Accessing an Object’s Keys, Values, and Entries in JavaScript

Object.keys(obj) → returns an array of a given object’s property names.
Object.values(obj) → returns an array of a given object’s own property values.
Object.entries(obj) → returns an array of a given object’s own string-keyed property [key, value] pairs.

var user = {

    name : "John",

    profession : "👨‍⚕️",

    salary  : 10000

Object.keys(user); // ["name", "profession", "salary"]

Object.values(user); // ["John", "👨‍⚕️", 10000]

Object.entries(user);

//output
0: (2) ["name", "John"]
1: (2) [“profession”, “👨‍⚕️”]
2: (2) [“salary”, “10000]
length: 3

All the above three methods return only the enumerable property of the object.

var user = {
    name : "John"
}

Object.defineProperty( user , 'salary', {
   value: 10000,
   enumerable: false
});

In the above code, we define a property salary and set enumerable property as false.This will make the salary hidden from the Object.keys.

Object.keys(user); ["name"]

Object.values(user); ["John"]

Object.entries(user); //  ["name", "John"]

We cannot loop through the symbol properties of the object.

var user = {
    name : "John"
}


let Passcode = Symbol("Passcode");

user[Passcode] = "1234";

Now we have set the symbol as a property of the object, but this will not be accessible using the three methods above.

Object.keys(user); //["name"]

Object.values(user); // ["John"]

Object.entries(user); //  ["name", "John"]

To access the symbol property of the object, we can use getOwnPropertySymbols().

Object.getOwnPropertySymbols(user); //[Symbol(Passcode)]

We can use for… as an alternative to the above methods.

var user = {
    name : "John",
    age  : 25
}

for(const property in user) {
    console.log(`user[${property}] = ${user[property]}`);
}

//output

user[name] = John
user[age]  = 25

Using map with Object.entries.

var user = {
    name : "John",
    age  : 25
}

let entries = Object.entries(user);

entries.map( ([prop, val]) => console.log(prop, val));

Alternatively, we can also use forEach.

var user = {
    name : "John",
    age  : 25
}

let entries = Object.entries(user);

entries.forEach( ([prop, val]) => console.log(prop, val));

Using for…of with Object.entries:

var user = {
    name : "John",
    age  : 25
}

let entries = Object.entries(user);

for(const [prop, val] of entries) {
    console.log(prop, val);
}

References:

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