javascript-the-movie/data.html at master · katophelix/javascript-the-movie · GitHub

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<!DOCTYPE html>

<html xmlns= xml:lang="en-US" lang="en-US">
<!--<![endif]-->

<head>
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  <title>Functions in JavaScript</title>


  <meta name="description" contect="A visual representation of Javascript variables, funtions and loops. This lesson is functions"

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            <h1 class="title" style="font-size: 3em;">Datatypes in Javascript</h1>
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                <div class="entry-content">
                <p>  Strings: A string (or a text string) is a series of characters like "John Doe".

                  Strings are written with quotes. You can use single or double quotes:</p>
                  <pre><code class="language-javascript" style="width: 100%;">var carName1 = "Volvo XC60";   // Using double quotes
                                      var carName2 = 'Volvo XC60';   // Using single quotes
                                    </code></pre>

               <p>  Numbers: JavaScript has only one type of numbers.

                  Numbers can be written with, or without decimals.</p>
                  <pre><code class="language-javascript" style="width: 100%;">
var x1 = 34.00;     // Written with decimals
var x2 = 34;        // Written without decimals
</code></pre>
                 <p> Booleans: Booleans can only have two values: true or false.</p>
                  <pre><code class="language-javascript" style="width: 100%;">
                                          var x = 5;
var y = 5;
var z = 6;
(x == y)       // Returns true
(x == z)       // Returns false
</code></pre>
                <p>  Arrays: JavaScript arrays are written with square brackets.

                  Array items are separated by commas.

                  The following code declares (creates) an array called cars, containing three items (car names):
                </p>
                  <pre><code class="language-javascript" style="width: 100%;">
                                          var cars = ["Saab", "Volvo", "BMW"];

                                        </code></pre>
                <p> Objects: JavaScript objects are written with curly braces {}.

                  Object properties are written as name:value pairs, separated by commas.</p>
                  <pre><code class="language-javascript" style="width: 100%;">
                                          var person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"};

                                        </code></pre>
                 <p> The typeof Operator:You can use the JavaScript typeof operator to find the type of a JavaScript variable.

                  The typeof operator returns the type of a variable or an expression.</p>
                  <pre><code class="language-javascript" style="width: 100%;">
                                          typeof ""             // Returns "string"
                                          typeof "John"         // Returns "string"
                                          typeof "John Doe"     // Returns "string"
                                          typeof 0              // Returns "number"
typeof 314            // Returns "number"
typeof 3.14           // Returns "number"
typeof (3)            // Returns "number"
typeof (3 + 4)        // Returns "number"

                                        </code></pre>
                                       <p>Undefined:
A variable without a value, has the value undefined. The type is also undefined.

Any variable can be emptied, by setting the value to undefined. The type will also be undefined.</p>
<pre><code class="language-javascript" style="width: 100%;">
   var car;    // Value is undefined, type is undefined

  car = undefined;    // Value is undefined, type is undefined
</code></pre>

<p>Empty Values:
An empty value has nothing to do with undefined.

An empty string has both a legal value and a type.</p>
<pre><code class="language-javascript" style="width: 100%;">
  var car;    // Value is undefined, type is undefined

</code></pre>

<p>Null:
In JavaScript null is "nothing". It is supposed to be something that doesn't exist.

Unfortunately, in JavaScript, the data type of null is an object.

You can consider it a bug in JavaScript that typeof null is an object. It should be null.

You can empty an object by setting it to null:You can also empty an object by setting it to undefined.</p>

<pre><code class="language-javascript" style="width: 100%;">
  var person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"};
person = null;    // Now value is null, but type is still an object
var person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"};
person = undefined;   // Now both value and type is undefined
</code></pre>

<p>Difference Between Undefined and Null
  undefined and null are equal in value but different in type:</p><pre><code class="language-javascript" style="width: 100%;">
    typeof undefined           // undefined
    typeof null                // object

    null === undefined         // false
    null == undefined          // true
  </code></pre>

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                  <p><span class="dropcap">J </span>avaScript
                   variables can hold many data types: numbers, strings, booleabs, arrays, objects and more:


                    To be able to operate on variables, it is important to know something about the type.
                  </p>


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