Variable Naming Rules in TypeScript

TL ; DR:

• In TypeScript, we use the camelCase convention to name our variables. It implies separating different words with capital letters, like this:

  let companyName = "Apple";
  
  let foundingYear = 1976;
  
  let isUnicorn = true;
  
  let numberOfEmployees = 137000;
  

  
  

Full lesson:

Variable names must consist ONLY of letters, numbers and underscores and they must start with a letter or underscore.

Bad variable names:

let 18spam;
let x.15;

If you try to create a variable with any of these names, the TypeScript compiler will report a syntax error.

Naming conventions: camelCase and snake_case

Sometimes a variable name might consist of multiple words, for example if you want to store the first name of a person. You might be tempted to separate those names by whitespaces, like this:

let first name = "Kate";

The compiler will report a syntax error for this code too.

When you name your variables, you want to use one of these two conventions:

snake_case = separate different words with an underscore (_), like this:

let first_name = "Jane";
let last_name = "Doe";

camelCase = separate different words with capital letters, like this:

let firstName = "Jane";
let lastName = "Doe";

It's important to be consistent with the casing technique you use. Do not combine both of them in the same code, like this:

let first_name = "Jane";
let lastName = "Doe";

Case sensitive:

Variable names are case sensitive:

let name = "Kate";
let Name = "Andy";
let NAME = "George";

console.log(name, Name, NAME); // Output: Kate Andy George

Although TypeScript allows us to do this, it's always confusing and a bad coding practice to differentiate variable names just by case!

Mnemonic Variable Names:

Since we programmers are given a choice in how we choose our variable names, there is a bit of "best practice".

Sometimes we want them short like x and y, but sometimes we want them descriptive, especially if they are important.

Here is a great example:

let a = 25;
let b = 13;
let c = a * b;
console.log(c);

compared to:

let hours = 25;
let rate = 13;
let pay = hours * rate;
console.log(pay);

TypeScript understands and is happy with both of these pieces of code. But it's clearly which version makes your reader happier.