[JS] 03. Type

03_Type.html

<script>
//Types in JavaScript fail into two categories; primitivesand objects.
//Primitive types include: String, Number, Boolean, null, undefined

/////// String ///////
// Strings can be created with double or single quotes.
var a = "I am a string";
var b = 'So am I!';

//Sometimes a string may contain quotation marks.
var statement1 = 'He said "JavaScript is a awesome!"';
var statement2 = "He said \"JavaScript is a awesome!"";
////////////////////////

/////// Number ///////
//Numbers are any whole or floating point integer.
var num1 = 100;
var num2 = 100.10;
var num3 = 0.10;
//////////////////////

/////// Boolean ///////
//Boolean values.
var okay = true;
var fail = false;
///////////////////////

/////// null and undefined ///////
//Define a null value. Null types are values  that represent the absence of a value
var foo = null;

//Undefined types represent a state in which no value has been assigned at all.
//This type is created in two ways: by using the undefined keyword or by not defining a value at all.
var bar1 = undefined;
var bar2;
//////////////////////////////////

/////// Objects ///////
//Creating an object with the constructor:
var person1 = new Object;
person1.firstName = "John";
person1.lastName = "Doe";
console.log(person1.firstName + " " + person1.lastName);

//Creating an object with the object literal syntax:
ver person2 = {
        firstName = "Jane";
        lastName = "Doe";
};
console.log(person2.firstName + "" + person2.lastName);

//obejcts can also have objects as a property.
var people = {};
people.person1 = person1;
people["person2"] = person2;
console.log(people["person1"].firstName);
console.log(people.person2.firstName);

//Properties that have not been created are undefined.
var person = {name: "John Doe"};
console.log(person.email); //undefined
/////////////////////////////////

/////// Array ///////
//Creating an array with the constructor:
var foo = new Array;

//Creating an array with the array literal syntax:
var bar = [];

//The array literal returns a foo.length value of 1:
var foo = [100];
console.log(foo[0]); //100
console.log(foo.length); //1

//The array constructor returns a bar.length value of 100:
var bar = new Array(100);
console.log(bar[0]); //undefined
console.log(bar.length); //100

//Using the push(), pop(), unshift() and shitf() methods on an array.
var foo = [];
foo.push("a");
foo.push("b");
console.log(foo[0]); //a
console.log(foo[1]); //b
console.log(foo.length); //2
foo.pop();
console.log(foo[0]); //a
console.log(foo[1]); //undefined
console.log(foo.length); //1
foo.unshift("z");
console.log(foo[0]); //a
console.log(foo[1]); //undefined
console.log(foo.length); //1
//////////////////////////

//Using JavaScript's type of operator to test for primitive types:
var myValue= [1,2,3];
console.log(typeof myValue === "string"); //false
console.log(typeof myValue === "number"); //false
console.log(typeof myValue === "undefined") //false
console.log(typeof myValue === "boolean"); //false
console.log(typeof myValue === "object") //true

//Using strict equality operator to check for null:
console.log(myValue === null); //false
</script>