Day 1. Introduction

On day 1, I learned the basics of the basics of JavaScript. I wrote some notes on my notebook, and this post will contain features that I think are important to remember.

header image TIL

1. console.log()

  • can take multiple arguments
  • the arguments are strings(texts)
    • single quotes(‘ ‘), double quotes(“ “), back-ticks(``)

2. Comments

  • single line comment 
    // this is a single line comment.
  • multiline comment 
    /*
you can put multiple lines of comments,
using these symbols.
*/

3. Arithmetics

On console(how to open:Ctrl+Shift+I), I can use these operators without console.log, but in text editor I should use console.log.

  • multiplication(*)
  • division(/)
  • addition(+)
  • subtraction(-)
  • modulus(%) - finding remainder
  • exponentation(**) ex) 3 ** 2 = 9

4. Adding Javascript to a web page

1) Inline script

<body>
  <button onclick = "alert('Welcome!')">Click me<button>
</body>

2) Internal script

  • could be written in both head/body
<script>
  console.log('Welcome!');
</script>

3) External script (create an external JavaScript file)

  • could be written in both head/body
<body>
  <script src = "introduction.js"></script>
</body>
  • before the closing tag(</body>) is recommended place to put JavaScript code

4) Multiple external scripts

  • you can add several JS files
  • ⚠️your main.js file should be below all other scripts(should be written last)


5. Introduction to Data Types

Primitive Types

  • Numbers - both integers(-,0,+) and float-point numbers
  • Strings - any data types under ‘ ‘, “ “, ``
  • Boolean - true / false
  • undefined
    • default value if we don’t assign any value to a variable
    • if a function is not returning anything, it returns undefined
  • null - an empty value


6. Variables

To declare a variable

A variable is a container of data. It stores the memory data of the location. When a variable is declared, the memory space is reserved. When the variable is assigned to a value(= a data), the memory space is filled.

To declare variable, we can use var, let, and const. var is not recommended, let is for variables that changes at a different time, and const is for datat that doesn’t change at all(e.g. PI, gravity).

Variable naming rules

The name of a variable…

  • doesn’t begin with number
  • doesn’t allow special characters except $ and _
  • follows a camelCase convention(cf. CamelCase for declaring classes)
  • doesn’t have space between words
/* 
'=' is called an assignment operator,
and the value is called an assigned data.
*/
let nameOfVariable = value;
  • Variables can be declared in one line seperated by comma, but it’s recommended to use a seperate line to make the code more readable.

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