How to Use Primitive Types in TypeScript: string, number, and boolean

TLDR TypeScript has 7 primitive types: string , number , boolean , null , undefined , bigint , and symbol . You use them to tell TypeScript what kind of value a variable holds. You write them in lowercase. TypeScript can often figure out the type for you. But knowing how each one works is key to writing safe and clear code. What Are Primitive Types? Primitive types are the simplest building blocks in TypeScript. Every piece of data in your program starts with one. They hold a single value. They are not objects. You cannot add methods or properties to them directly. TypeScript has 7 primitive types in total: Type What It Holds string Text like names, messages, or IDs number Any number: integers, decimals, negatives boolean Only true or false null An intentional empty value undefined A value that was never assigned bigint Very large whole numbers symbol A unique identifier value This article covers all 7. You will use string , number , and boolean the most in everyday TypeScript code. How to Use the string Type A string holds text. Use it for names, messages, emails, URLs, and any other text data. Basic string annotation let firstName : string = " Alice " ; let greeting : string = " Hello, world! " ; let empty : string = "" ; Three ways to write strings TypeScript supports the same three string styles as JavaScript: let single : string = ' Single quotes work fine ' ; let double : string = " Double quotes work too " ; let template : string = `Template literals with ${ firstName } ` ; Template literals (backticks) let you insert values inside a string with ${} . TypeScript checks the types of those inserted values too. let age : number = 30 ; let message : string = `I am ${ age } years old` ; // TypeScript checks that 'age' is compatible here What TypeScript catches with strings let name : string = " Alice " ; name = 42 ; // Error: Type 'number' is not assignable to type 'string'. name = true ; // Error: Type 'boolean' is not assignable to type 'string'. Once a variable