Marusya's School Notes

JavaScript Data Types

JavaScript variables can hold many data types, such as numbers, strings, arrays, objects, booleans, and more:

   var length = 16; <===== This is a Number Data Type
   var lastName = "Johnson"; <===== This is a String Data Type
   var cars = ["Saab", "Volvo", "BMW"]; <===== This is a Array Data Type
   var x = {firstName:"John", lastName:"Doe"}; <===== This is a Object Data Type

The Concept of Data Types

In programming, data types is an important concept. To be able to operate on variables, it is important to know something about the type. Without data types, a computer cannot safely solve this:
var x = 16 + "Volvo";

Does it make any sense to add "Volvo" to sixteen? Will it produce an error or will it produce a result? JavaScript will treat the example above as:
var x = "16" + "Volvo";
When adding a number and a string, JavaScript will treat the number as a string. Therefore, the value of x is 16Volvo. Note: In the case of var x = "Volvo" + 16;, the value is Volvo16.

JavaScript evaluates expressions from left to right. Different sequences can produce different results:

var x = 16 + 4 + "Volvo"; (The result: 20Volvo)
var x = "Volvo" + 16 + 4; (The result: Volvo164)

In the first example, JavaScript treats 16 and 4 as numbers, until it reaches "Volvo". In the second example, since the first operand is a string, all operands are treated as strings.