Module 1 : Classless Objects

Section 1 : What is an object?

Primitive data types

https://developer.mozilla.org/en-US/docs/Glossary/Primitive

• a type is a certain value can be checked with the typeof command. Note that typeof returns the name of the data type as a string.
• If we have not explicitly assigned any value to a declared variable, it contains an undefined value by default.

console.log(typeof 2.5); // -> number
console.log(typeof "one two three"); // -> string
console.log(typeof false); // -> boolean

let nr = 2.5; 
nr = nr / 2;
console.log(typeof nr); // -> number

let name1;
console.log(typeof name1); // -> undefined

Array as a complex type

https://www.codinn.dev/javascript/complex-data-types

• Complex types an ordered set of different values can be placed in one variable.
• In the case of an array, individual values placed in a single variable are called elements, and are referred to by a number specifying their position in the collection (i.e. an index).
• In JavaScript, indexes start at 0, so the first element will have an index of 0, the second an index of 1, and so on.
• As a reminder, arrays are most easily created using square brackets (although this is not the only way to create them).

let a = [10, 20, "en to tre", true, 50];
a[4] = a[4] * 2;
console.log(a[0]);    // -> 10
console.log(a[2]);    // -> en to tre
console.log(a[4]);    // -> 100

An object as a different type of array

• From a formal point of view, an object can be treated as a special kind of array.
• We don’t refer to the individual elements of an object by means of indexes, which define their position in the collection, but by means of keys (i.e. we "associate" an element with a key).