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Lesson 1: How to run, variables and comments

Contents

  1. How to run JavaScript
  2. Variables
  3. Comments
  4. Built-in notation

1. How to run JavaScript

  • Download the extensions for JavaScript and Live Server
  • Create 2 files: main.js and index.js
  • In index.js, we type "html:5" to print out this code:
     <!DOCTYPE html>
     <html lang="en">
     <head>
          <meta charset="UTF-8">
          <meta name="viewport" content="width=device-width, initial-scale=1.0">
          <title>Document</title>
     </head>
     <body>
     </body>
     </html>
  • In main,js, we type:
     alert('Hello World!'); // alert function

     OR:

     console.log('Hello World'); // print function
  • Finally, we run "Live Server" or console to see the result

2. Variables

  • To declare a variable, we can use the keyword var which means 'variable':
     var fullName; // Declare a variable
     fullName = 'Pham Gia Phuc'; // Assign a value to a variable

     console.log(fullName); // Print out the value in the console
  • To declare multiple variables, we use semicolons:
     var name = 'John', age = 18, address = 'Vietnam';

     OR:
     
     var name = 'John',
          age = 18,
          address = 'Vietnam';
  • Naming variable rules:
     // Correct naming variables
     var name = 'John';
     var first_name = 'Alexander';
     var fullName = 'John Alexander';
     var f8 = 8;

     // Incorrect naming variables
     var first-name = 'Alexander';
     var 8f = 8;

The variable's name must be specific and accurate in the function to have a clean and performance code.

  • Using the single quote or double quotes in string variable type are no different at all, but recommned to use double quotes for better readability:
     var name = 'John' // Single quote
     var name = "John" // Double quotes
  • Assigning value from this variable to another variable:
     var a = 1;
     var b = a; // 1

3. Comments

  • Using comments to increase the readability of the code.
  • How to use:
     // Single line

     /**
      * Multiple lines
     */

4. Built-in Notation

  • 6 standard built-in objects:
     // Alert
     alert("Hello World!");
     // Console
     console.log("Hello World!");
     // Confirm
     confirm("Press a button!"); 
     // Prompt
     prompt("Your age?");
     // Set timeout
     setTimeout(function() {
          console.log("Hello World!"); // Print out the "Hello World" after 1s
     }, 1000 // 1000ms
     )
     // Set interval
     setInterval(function() {
          console.log("Hello World!"); // Print out multiple times the "Hello World" after 1s
     }, 1000 // 1000ms
     )