Comments are lines of code that JavaScript will intentionally ignore.
There are two ways to write comments in JavaScript:
Using // will tell JavaScript to ignore the remainder of the text on the current line. This is an in-line comment:
// This is an in-line comment. You can make a multi-line comment beginning with /* and ending with */. This is a multi-line comment:
/* This is a multi-line comment */
JavaScript provides eight different data types which are undefined, null, boolean, string, symbol, bigint, number, and object.
We tell JavaScript to create or declare a variable by putting the keyword var in front of it, like so:
var ourName; creates a variable called ourName. In JavaScript we end statements with semicolons. Variable names can be made up of numbers, letters, and $ or _, but may not contain spaces or start with a number.
When JavaScript variables are declared, they have an initial value of undefined. If you do a mathematical operation on an undefined variable your result will be NaN which means "Not a Number". If you concatenate a string with an undefined variable, you will get a literal string of undefined.