JavaScript Built-in Object Methods

We have already seen how to create objects and object methods, but there are built-in methods that JavaScript makes available for use.

Below are examples of a few methods:

const person = {
    name: 'Bob', 
    age: 54, 
    country: 'London'
};

const toArray = Object.values(person);
console.log(toArray); // [ 'Bob', 54, 'London' ]

const person = {
    name: 'Bello', 
    age: 27, 
    country: 'Nigeria'
};

const toStr = JSON.stringify(person);
console.log(toStr);
// {"name":"Bello","age":54,"country":"Nigeria"}

toStr[0]; // '{'
toStr[1]; // "
toStr[2]; // n

JSON.stringify will not stringify functions:

const person = {
    name: 'Bello', 
    age: function() {
      return 27;
    }, 
    country: 'Nigeria'
};

const toStr = JSON.stringify(person);
console.log(toStr);
// {"name":"Bello","country":"Nigeria"}

We have to convert the function to string (toString) first.

const person = {
    name: 'Bello', 
    age: function() {
      return 27;
    }, 
    country: 'Nigeria'
};

const str = person.age.toString();
console.log(str);
/* 
function() {
    return 27;
}
 */

const toStr = JSON.stringify(person);
console.log(toStr);
/* 
function() {
    return 27;
}
{"name":"Bello","country":"Nigeria"}
 */

Both arrays and objects are non-primitive data types as objects. Therefore a few object methods can work on arrays also. Like JSON.stringify()

const arr = [ 'Bello', 27, 'Nigeria' ];

const toStr = JSON.stringify(arr);
console.log(toStr); // ["Bello",27,"Nigeria"]

toStr[0]; // "["
toStr[2]; // "B"

More on arrays later.

const person = {
    name: 'Bob', 
    age: 54, 
    country: 'London'
};

const hasProp = person.hasOwnProperty('name'); 
hasProp; //true

Object.assign() copies all objects properties into a new object

const obj1 = {
  a: 1,
  b: 2,
  c: 3
};

const obj2 = {
  d: 4,
  e: 5
}

const newObj = Object.assign(obj1, obj2);
newObj; // { a: 1, b: 2, c: 3, d: 4, e: 5 }

The general syntax is:

newObj = Object.assign(obj1[, obj2, ...,objN]);

A similar new object property name overrides the old object property name.

Object.assign(oldObj, newObj)

const obj1 = {
  a: 1,
  b: 2,
  c: 3
};

const obj2 = {
  c: 100,
  e: 5
}

const newObj = Object.assign(obj1, obj2);
newObj; // { a: 1, b: 2, c: 100, e: 5 }

c: 100 overrides c: 3

const person = {
    name: 'Bob', 
    age: 54, 
    country: 'London'
};

const objKeys = Object.keys(person);
console.log(objKeys); // [ 'name', 'age', 'country' ]

The entries method used on an object converts the object, property keys, and property values to an array.

Syntax:

[ [key1, value1], [key2, value2], ...[keyN], [valueN] ]

const person = {
    name: 'Bob', 
    age: 54, 
    country: 'London'
};

const objEntries = Object.entries(person);
console.log(objEntries); 
// [ [ 'name', 'Bob' ], [ 'age', 54 ], [ 'country', 'London' ] ]

objEntries[1]; // [ 'age', 54 ]
objEntries[1][0]; // "age"