Lesson 9 - Values and Variable

I Will use a 'Person' for the example. eg. first name, last name, age, height etc

• Value is a piece of data

console.log("Jonas");
console.log(23);

For this example "Jonas" is a value. 23 is also a value.

A value is basically the smallest piece of information we have in JavaScript.

One extremely useful thing about a value is that they can be stored in variables. eg

let firstName = "Jonas";
let age = 23;

The good thing about variable is that we can use them in multiple places.

console.log(`First name: ${firstName}, Age ${age};`);

if (age >= 21) {
  console.log(`${firstName} is old enough to drink.`);
} else {
  console.log(`${firstName} is only ${age}, too young to enter this bar.`);
}

Also if we want to change the name, we can do that easily byt just changing the value in one place.

let firstName = "Matilda";

Naming Conventions

• Camel Case: Words are joined without spaces, with the first letter of each word (except the first) being uppercase. Example: firstName this is the standard in the JavaScript world.
• Pascal Case: Similar to camel case but all words start with an upper case. Example FirstName
• Snake Case: Words are joined with an underscore(_). Example first_name this is more popular in other languages like Ruby.

There are also some hard rules that you must also use. You cannot start a variable with a number. HOWEVER it can contain numbers.

let firstName = "Jonas";
let name1 = "Matilda";
let 1stName = "Bob";

Variables can only contain numbers, letters, underscore or dollar ($)

For example if I do let jonas&bob = "JB"; it will error out with a SyntaxError. It would be best to use underscore let jonas_bob = "JB";

Other syntax errors could be that you used a Reserved Keyword as your variable name.

let new = "New Car";

Another convention is you should never start a variable with an uppercase letter. It not illegal. its just we use this for a specific case which is Object-Oriented Programming (More in later Lessons).

Variable that are in all Uppercase are reserved for constants (Variable that do not change). eg

let PI = 3.1415;

For the final convention make sure your name is descriptive. It help you understand your code better when you comeback to it.

Summarize

A variable is a named box that we can store a value in.