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variable and constant
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‎02. Start Coding/img/img-01.png

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‎02. Start Coding/img/img-2.png

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‎02. Start Coding/note.html

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@@ -59,9 +59,30 @@ <h4 class="fs-4 mt-4">JavaScript Ouput</h4>
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document.getElementById("output").innerHTML = "Hello, World!";
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</code>
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<p>Use <code>script</code> tag for writng javacript code in html</p>
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<p class="mb-0">Use <code>script</code> tag for writng javacript code in html</p>
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<p>Also you can use externel file write javacript code with script link</p>
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<img class="img-fluid col-md-6" src="img/img-01.png" alt="">
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<h4 class="fs-4 mt-4">JavaScript Ouput</h4>
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<p>In computer programming, a comment is a programmer-readable explanation or annotation in the source code of a computer program. They are added with the purpose of making the source code easier for humans to understand, and are generally ignored by compilers and interpreters.[1][2] The syntax of comments in various programming languages varies considerably.</p>
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<code>//Single Line Comment</code>
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<p></p>
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<code>/*
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Mutiline <br>comment
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*/</code>
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<h4 class="fs-4 mt-4">JavaScript User Input</h4>
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<p class="mb-0">We can use prompt function for javacript user input</p>
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<code>
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var x;<br>
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x = prompt("Enter your name: ");<br>
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console.log(x);<br>
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</code>
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<p class="m-0"><b>Output</b></p>
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<code>Aktaruzzaman</code>
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<p><b>Example:</b></p>
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<img src="img/img-2.png" class="img-fluid col-md-6" alt="">
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</div>
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‎03. Variables and Constant/index.html

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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<title>Document</title>
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</head>
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<body>
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<h1 id="showMessage"></h1>
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<!-- link javacript file -->
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<script src="js/script.js"></script>
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</body>
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</html>

‎03. Variables and Constant/js/script.js

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//Declare variables
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var var1 = 10;
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console.log(var1);
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//Reassign variables
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var var2 = 10;
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var2 = 32;
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console.log(var2);
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//Assign variables in another variable
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var2 = var1;
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console.log(var1);
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// Declare const
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const CONS = 1;
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console.log(CONS);
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//Incorrect declaration constant
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// const NUM;
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// NUM = 1;
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var a;
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var b = a;
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a =34;
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console.log(b);

‎03. Variables and Constant/note.html

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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<title>Java Script Basics</title>
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<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.3.3/dist/css/bootstrap.min.css" rel="stylesheet">
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<style>
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* {
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margin: 0;
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padding: 0;
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}
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</style>
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</head>
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<body>
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<div class="container">
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<div class="row">
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<h4 class="fs-4 mt-4">Variable</h4>
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<p>We can use var and let for declar a variable in javascript. var and let have some different. We can learn
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it after ES6 lesson</p>
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<p class="mb-0"><b>Declare a Variable</b></p>
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<code class="mb-3">
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var myName = "Aktaruzzaman";<br>
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var number = 1;
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</code>
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<p class="mb-0"><b>Reassign Variable</b></p>
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<code class="mb-3">
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var myName = "Aktaruzzaman";<br>
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myName = 35;<br>
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console.log(myName);<br><br>
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<b>ouput:</b>
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35
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</code>
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<p class="mb-0"><b>Assign Variable in Another Variable</b></p>
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<code class="mb-3">
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var1 = 10; <br>
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var2 = 30; <br>
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var1 = var2; <br>
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console.log(var1, var2);
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<br><br>
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<b>ouput: </b>
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<span>10 10</span>
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</code>
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<p class="mb-0"><b>JavaScript Identifiers(Rules)</b></p>
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<pre>
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All JavaScript variables must be identified with unique names.
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These unique names are called identifiers.
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Identifiers can be short names (like x and y) or more descriptive names (age, sum, totalVolume).
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The general rules for constructing names for variables (unique identifiers) are:
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* Names can contain letters, digits, underscores, and dollar signs.
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* Names must begin with a letter.
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* Names can also begin with $ and _ (but we will not use it in this tutorial).
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* Names are case sensitive (y and Y are different variables).
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* Reserved words (like JavaScript keywords) cannot be used as names.
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</pre>
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<p class="mb-0"><b>JavaScript Identifiers(Rules)</b></p>
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<pre>
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* The const keyword was introduced in ES6 (2015)
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* Variables defined with const cannot be Redeclared
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* Variables defined with const cannot be Reassigned
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* Variables defined with const have Block Scope
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<b>Always declare a variable with const when you know that the value should not be changed.</b>
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</pre>
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<b>Example:</b>
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<p class="mb-1">Correct Example:</p>
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<code>
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const PI = 3.14159265359
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</code>
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<p class="mb-1">Incorrect Example:</p>
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<code>
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const PI = 3.141592653589793;<br>
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PI = 3.14; // This will give an error <br>
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PI = PI + 10; // This will also give an error <br>
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</code>
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<p class="m-0 mt-3"><b>Keywords:</b></p>
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<p>In programming, a keyword is a word with a specific meaning and purpose that is reserved by a programming language. Keywords are used in the syntax of a program to define its structure and flow, and to specify the operations it should perform. They are also known as reserved words.</p>
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</div>
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</div>
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<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.3.3/dist/js/bootstrap.bundle.min.js"></script>
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<p></p>
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</body>
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</html>

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