# JavaScript The console is part of the web browser and allows you to log messages, run JavaScript code, and see errors and warnings. \\ ### JS Basics Example function used to generate output to the console: ```javascript console.log("Hello Humans!"); ``` Enclosed text in quotes: ```javascript console.log("I love free cyber training"); ``` Quotes are not needed for numbers: ```javascript console.log(1337); ``` The console.log() function can be used as many times as needed: ```javascript console.log("Hello Humans!"); console.log("Take me to your leader"); ``` ### JavaScript in HTML You can add JavaScript code in an HTML document using the \ ``` Alert Box display messages with the alert() function ```html ``` ### Comments Comments are used to describe code and other information\ \ A single-line comment starts with `//` Multi-line comments start with `/*` and end with `*/` making everything in between a comment 
//I wonder if I can display two messages in the same script tag

/* The code below
should suffice
for testing */

<body>
    <script>
      console.log("JavaScript in HTML");
      alert("I think I can learn XSS now");
    </script>
</body>
### Logic JavaScript uses the basic programming operators for math such as `+`. `-`, `/`, `*`, including `(`, and `)`, for order of operations. ```javascript /* 30 days 1 day = 24 hours 1 hour = 60 minutes 1 minute = 60 seconds */ //Aproximately how many seconds are in a year? console.log(60*60*24*30); ``` Increment operator `++` adds 1 to a variable ```javascript let count = 0; count++; console.log(count); ``` Decrement operator `--` subtracts 1 from a variable ```javascript let score = 100; score--; score--; console.log(score); ``` Combining Arithmetic operators with increment/decrement operators looks like the sample below: ```javascript let x = 8; x++; x/=3; console.log(x); //Output should equal 3 ``` ### Variables * variable names must begin with a letter, an underscore `_` or a dollar sign `$` * variable names cannot contain spaces * variable names can only contain letters, numbers, underscores, or dollar signs. * variable names are case-sensitive, which means that, for example, Name and name variables are different Create a variable (initialize) in JS with `let` or `var`: ```javascript let name; name = "Martian"; ``` OR ```javascript let name = "Martian"; let number = 1337 ``` Note: the use of let is recommended instead of var when decalring variables Remembering the definition of variable, remember that they can change on they fly: ```javascript let num = 7331; num = 1337; //num = 7; console.log(num); ``` ### Constants Constants must have a value when declared and they cannot change their value. ```javascript const cyberpsace = 'green'; console.log(color); color = 'blue'; //confirm this will not work ``` The `typeof` operator checks the value to its right and *returns*, or passes back, a string of the data type. ```javascript const unknown1 = 'foo'; console.log(typeof unknown1); // Output: string const unknown2 = 10; console.log(typeof unknown2); // Output: number const unknown3 = true; console.log(typeof unknown3); // Output: boolean ``` ## Conditional (Ternary) operator Conditional, or ternary, operators assign a value to a variable, based on some condition. This operator is frequently used as an alternative to an `if else` statement. This is what the syntax would look like: ```javascript variable = (condition) ? value1: value2 ``` It takes three operands: a condition followed by a question mark `?`, then an expression to execute if the condition is true followed by a colon `:`, and finally, the expression to execute if the condition is false. ```javascript let lightyears = 42; let allowedDistance = (lightyears < 5) ? "Too close to Earth": "Welcome to the void"; console.log(allowedDistance); ``` For this example below, if the total amount is equal to or above 300 it will be discounted by 15%. ```javascript let cost = 400; cost = (cost >= 300) ? cost * 0.85 : cost; console.log(cost); ``` ## Loops ### For Loop The `for` loop has the following syntax: ```javascript for (initializer; condition; final-expression) { // code to run } ``` The initializer is a variable, which increments the number of times the loop has run. The condition is used to stop the loop. The final expression is run each time after the loop's code has run. It is usually used to increment the variable used in the condition. Each run of the loop is called an **iteration**. Here is an example of a `for` loop outputting the number 1 to 10: ```javascript for (let i = 1; i <= 10; i++) { console.log(i); } ``` The loop creates a variable called `i` and initializes it to 1. Then, after each iteration, it increments the `i` variable by 1. The loop stops when `i` reaches 11, breaking the condition. Here is another loop in which each time the player shoots, the number of bullets should be decreased by 1. ```javascript for(let i=5; i>=0; i-=1) { console.log(`Bullets: ${i}`); } ``` ### While Loop