JavaScript Data Types

There are 7 data-types in JavaScript. 6 of those are "primitives" and the other is the "object" data type. Technically, arrays and functions are just unique implementations of an object, and therefore, are objects.

---

Primitives

Definitions from MDN Web Docs:

• Boolean

  Boolean represents a logical entity and can have two values: true, and false.

• Null

  Meaning, nothing. The Null type has exactly one value: null.

• Undefined

  A variable that has not been assigned a value has the value undefined.

• Number

  According to the ECMAScript standard, there is only one number type... There is no specific type for integers. In addition to being able to represent floating-point numbers [decimals], the number type has three symbolic values: +Infinity, -Infinity, and NaN (not-a-number).

• String

  JavaScript's String type is used to represent textual data. It is a set of "elements" of 16-bit unsigned integer values. Each element in the String occupies a position in the String. The first element is at index 0, the next at index 1, and so on. The length of a String is the number of elements in it.

• Symbol (new in ECMAScript 6)

  Symbols are new to JavaScript in ECMAScript Edition 6. A Symbol is a unique and immutable primitive value and may be used as the key of an Object property. In some programming languages, Symbols are called atoms.

---

Exercise

Take some time to look at each data-type above ensuring that you can each define them all in your own words.

---

Objects

In JavaScript, all other data-types are technically objects (arrays and functions too). An object is essentially just a key-value pair of data.

var car = {
  color: 'red',
  wheels: 4
}

If we were to draw a diagram of this, we would see that that the var is referencing the object itself, which is a collection of properties, each referencing a primitive data-type (a string and an number).

Now, let's think about the implementation of an array:

var people = ['Aaron', 'Sean'];

If we were to diagram this, we would see a similar pattern, only with the array, our property keys are replaced with sequential indices:

---

Conclusion

Hopefully this is a brief review of concepts you already know! Let's move on to the next part of our overview.