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JavaScript arrays: a separate data type or Objects?
January 4, 2021

Are arrays a separate data type?

No, JavaScript arrays are not a separate data type. In JavaScript, arrays are objects.

Arrays are Objects

The JavaScript Array class is a global object.

Arrays are list-like objects whose prototype has methods to perform traversal and mutation operations.

Neither the length of a JavaScript array nor the types of its elements are fixed.

Arrays, then, are just a kind of object specialized for storing sequences of things.

If you evaluate typeof [], it produces “object”.


var cars = ["Audi", "Toyota", "Tesla"]
console.log(typeof(cars));

// object

You can see them as long, flat octopuses with all their tentacles in a neat row, labeled with numbers.

Arrays cannot use strings as element indexes but must use integers.


var cars = ["Audi", "Toyota", "Tesla"]
console.log(cars[0]);

// Audi

Using an invalid index number returns undefined.


var cars = ["Audi", "Toyota", "Tesla"]
console.log(cars[3]);

// undefined

Array elements are object properties in the same way that toString is a property (or a method).

But, trying to access an element of an array as follows throws a syntax error because the property name is not valid:


var cars = ["Audi", "Toyota", "Tesla"]
console.log(cars.0);

// SyntaxError

📌 JavaScript properties that begin with a digit cannot be referenced with dot notation and must be accessed using bracket notation.

Arrays are special kinds of objects.

Because of this, you can have variables of different types in the same Array.

You can have objects in an Array:


var cars = [
  {firstName:"John", lastName:"Doe", age:28},
  {firstName:"Yogesh", lastName:"Chauhan", age:28}
]
console.log(cars[1]);

// { firstName: 'Yogesh', lastName: 'Chauhan', age: 28 }

You can have functions in an Array:


var array_of_functions = [
  printFullName("Yogesh"),
  printFirstName("Yogesh"),
  ]

console.log(array_of_functions[0]);

function printFullName(name){
  return name + " Chauhan";
}

function printFirstName(name){
  return name;
}

// Yogesh Chauhan

You can have arrays in an Array:


var array_of_arrays = [ 
   ["a", "b"], ["a", 2], [4,100]
  ]

console.log(array_of_arrays[0]);

// [ 'a', 'b' ]

Sources

dreamhost

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