reading-notes

Class 6 Notes

JavaScript

Source:https://developer.mozilla.org/en-US/docs/Web/JavaScript

What is JavaScript? A lightweight, interpreted, or “just in time” compiled programming language. It is a scripting language that allows you to create dynamically updating content, control multimedia, animate images, and many other things.

Intro to JavaScript - basic output

Source: https://code-maven.com/introduction-to-javascript

Where is JS run? Traditionally inside web browsers, but more recently on the server as well (i.e. Node.js)
There’s 3 parts to JS:
1. The language itself
2. The “DOM API” - how it interacts with the various parts of a web page in a browser
3. The server API, provided by Node.js or another server-side system
Any text editor can be used
You can either embed the JS code inside the HTML file or put a line in the HTML file including the JS file, by adding ‘
Examples of how JS displays text as output:
1. ‘alert()” - pop-up with text
2. ‘document.write’ - changes the content of the page; embeds a snippet
3. ‘console.log’ - way to print debugging info through the JS console

JavaScript input with prompt and confirm

Source: https://code-maven.com/javascript-input-with-prompt-and-confirm

Ways to receive input with JS:
1. ‘prompt()” - shows a pop-up window with text and a textbox a user can fill in
2. ‘confirm()’ - pop-up that allows developer to ask “yes/no” question; an OK response returns ‘true’ and cancel or ESC returns ‘false’

JavaScript Variables

Source: https://www.w3schools.com/js/js_variables.asp

Variables are containers for storing data values. Example: x, y, and z are variables declared with ‘var’ ‘var x = 5; var y = 6; var z = x + y;’
There’s 4 ways to declare a JS variable:
1. var (1995 - 2015)
2. let : if you think the value of the variable can change
3. const : if you think the value of the variable can’t change
4. (nothing)

JS Identifiers

All JS variables must be identified with names, called identifiers
- Can be short names like x or y, or more descriptive like age, sum, totalVolume
General rules of naming variables:
1. Names can contain letters, digits, _ and $
2. Names must begin with a letter
3. Names can begin with $ and _
4. Names are case sensitive
5. Reserved word like JS keywords can’t be used
The Assignment Operator: The = is an “assignment” in JS, not an ‘equal to’ operator, different from algebra
JS Data Types: 1) text values (text strings), and 2) numbers
Declaring a JS Variable: Creating a variable is declaring a variable in JS
Declare a variable with ‘var’ or ‘let’, after which it has no value (it’s undefined)
to assign value, use ‘=’
you can declare many variables in one statement (separated with comma) - Example: ‘let person = “John Doe”, carName = “Volvo”, price = 200;’
or separate them on multiple lines - Example: ‘let person = “John Doe”; carName = “Volvo”; price = 200;’
Value = undefined - a variable without a value is ‘undefined’
Example, variable carName will be undefined here: ‘let carName;’
Re-declaring JS variables - if you re-declare a variable with ‘var’, it doesn’t lose it’s value, however, you cannot re-declare a variable declared with ‘let’ or ‘const’
Example: ‘let carName = “Volvo”; let carName;’
JS Arithmetic with algebra, you can do arithmetic with JS variables using operations like ‘=’ and ‘+’
If you put a number in quotes, however, the rest of the numbers are treated as strings and concatenated
JS Dollar Sign - The dollar sign is a letter, so identifiers with $ are valid variable names
not common in JS but sometimes used as an alias for the main function in a JS library
JS Underscore _: underscore is a letter, so identifiers with _ are valid variable names
not common in JS but sometimes used as an alias for private/hidden variables

Add to bookmark: https://www.youtube.com/playlist?list=PLzdnOPI1iJNcsRwJhvksEo1tJqjIqWbN-

Things I Want To Know More About

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URL: https://s-glass.github.io/reading-notes/102/class6notes