TypeScript Class 4

 

Legal and Illegal Variable Names in TypeScript

Variable naming is an important aspect of writing clean and maintainable code in TypeScript (or any programming language). There are specific rules and conventions you must follow to ensure your variable names are legal. This blog post will outline the guidelines for naming variables in TypeScript, highlighting what constitutes legal and illegal variable names.

Legal Variable Names

1. Start with a Letter, Underscore (_), or Dollar Sign ($): Variable names must begin with a letter (a-z, A-Z), an underscore (_), or a dollar sign ($).

   typescript
   let name = "Alice";
   let _age = 25;
   let $salary = 50000;
   

2. Contain Letters, Numbers, Underscores, or Dollar Signs: After the first character, variable names can include letters, numbers (0-9), underscores, and dollar signs.

   typescript
   let user1 = "Bob";
   let _totalAmount = 150.75;
   let $price_after_discount = 99.99;
   

3. Case Sensitivity: Variable names are case-sensitive, meaning myVar and myvar are considered different variables.

   typescript
   let myVar = "Hello";
   let myvar = "World";
   console.log(myVar); // "Hello"
   console.log(myvar); // "World"
   

4. Descriptive Names: While not a strict rule, using descriptive names for variables improves code readability and maintainability.

   typescript
   let firstName = "John";
   let numberOfItems = 10;
   

Illegal Variable Names

1. Starting with a Number: Variable names cannot begin with a number.

   typescript
   let 1stName = "Alice"; // SyntaxError
   

2. Using Reserved Keywords: Variable names cannot be reserved words or keywords in TypeScript, such as let, const, class, function, etc.

   typescript
   let let = 10; // SyntaxError
   let class = "Math"; // SyntaxError
   

3. Including Spaces: Variable names cannot contain spaces.

   typescript
   let first name = "Alice"; // SyntaxError
   

4. Special Characters (Other than $ and _): Variable names cannot contain special characters like !, @, #, %, ^, &, *, (, ), -, +, =, {}, [], ;, :, ,, <, >, /, ?, \, |, etc.

   typescript
   let user-name = "Bob"; // SyntaxError
   let user@domain = "alice@example.com"; // SyntaxError
   

Examples of Legal and Illegal Variable Names

Here are some examples to illustrate legal and illegal variable names:

Legal Variable Names:

typescript
let userName = "Alice";
let _userAge = 25;
let $userSalary = 50000;
let totalAmount1 = 150.75;
let user_name = "Bob";

Illegal Variable Names:

typescript
let 1stUser = "Alice"; // Illegal: starts with a number
let function = "login"; // Illegal: uses a reserved keyword
let user name = "Bob"; // Illegal: contains a space
let user-name = "Charlie"; // Illegal: contains a hyphen

Best Practices for Naming Variables

1. Be Descriptive: Use meaningful and descriptive names that clearly indicate the purpose of the variable.

   typescript
   let userName = "Alice";
   let numberOfItemsInCart = 10;
   

2. Use CamelCase for Multi-Word Variables: Adopt camelCase (first word lowercase, subsequent words capitalized) for variable names.

   typescript
   let firstName = "John";
   let totalAmountDue = 200.50;
   

3. Avoid Abbreviations: Avoid using abbreviations or single-letter names, except in loop counters or temporary variables.

   typescript
   let userAge = 30; // Better than "usrAg"
   

4. Consistency: Follow a consistent naming convention throughout your codebase to enhance readability and maintainability.

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Understanding and following the rules for legal variable names in TypeScript ensures your code is syntactically correct and easier to read. By adopting best practices for naming variables, you can write more maintainable and understandable code.