# Typescript - Tips & Tricks - typeof

> Today I want to start a series of tips and tricks about Typescript. I will try to publish two/three...

- **Author**: Luca Del Puppo (@puppo92) — AI Native Engineer at Nearform
- **Published**: Feb 15, 2021
- **Canonical URL**: https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-typeof/
- **Series**: TypeScript - Tips & Tricks (Part 1 of 21) — https://delpuppo.net/blog/series/ts-tips-and-tricks/
- **Series LLMs.txt**: https://delpuppo.net/blog/series/ts-tips-and-tricks/llms.txt
- **Category**: TypeScript
- **Tags**: typescript, webdev
- **Hashnode Mirror**: https://blog.delpuppo.net/typescript-tips-tricks-typeof
- **Dev.to Mirror**: https://dev.to/playfulprogramming/typescript-tips-tricks-typeof-nfi
- **Blog Index LLMs.txt**: https://delpuppo.net/blog/llms.txt

## Series Context: TypeScript - Tips & Tricks

- Part 1: [Typescript - Tips & Tricks - typeof](https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-typeof/) **(Current Article)**
- Part 2: [Typescript - Tips & Tricks - Literal Types](https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-literal-types/)
- Part 3: [Typescript - Tips & Tricks - keyof](https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-keyof/)
- Part 4: [Typescript - Tips & Tricks - Union and Intersection](https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-union-and-intersection/)
- Part 5: [Typescript - Tips & Tricks - Overloaded Functions](https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-overloaded-functions/)
- Part 6: [Typescript - Tips & Tricks - this parameter](https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-this-parameter/)
- Part 7: [Typescript - Tips & Tricks - any vs. unknown](https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-any-vs-unknown/)
- Part 8: [Typescript - Tips & Tricks - Optional modifier](https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-optional-modifier/)
- Part 9: [Typescript - Tips & Tricks - Index Signature](https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-index-signature/)
- Part 10: [Typescript - Tips & Tricks - readonly modifier](https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-readonly-modifier/)
- Part 11: [Typescript - Tips & Tricks - Readonly Array](https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-readonly-array/)
- Part 12: [Typescript - Tips & Tricks - Tuple](https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-tuple/)
- Part 13: [Typescript - Tips & Tricks - Non-null assertion operator](https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-non-null-assertion-operator/)
- Part 14: [Typescript - Tips & Tricks - Never type](https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-never-type/)
- Part 15: [Typescript - Tips & Tricks - Assert Function](https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-assert-function/)
- Part 16: [Typescript - Tips & Tricks - Type Guard](https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-type-guard/)
- Part 17: [Typescript - Tips & Tricks - Conditional Type](https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-conditional-type/)
- Part 18: [Typescript - Tips & Tricks - infer keyword](https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-infer-keyword/)
- Part 19: [Typescript - Tips & Tricks - Mapped Types](https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-mapped-types/)
- Part 20: [Typescript - Tips & Tricks - Advanced Types](https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-advanced-types/)
- Part 21: [Typescript - Tips & Tricks - Rest Parameters & Rest Arguments](https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-rest-parameters-rest-arguments/)

---

Today I want to start a series of tips and tricks about Typescript.
I will try to publish two/three tips & tricks a week.
Before start, I want to explain why I start this series.
I start this series because every day I see too many _any_ types in the typescript files and so I want to help the developers to learn better the typescript language.

## typeof
Today I start with the **typeof** operator.
Typeof is an operator used to detect the type of our variables.
A little preamble, typeof is also a javascript operator, but with typescript, it has superpowers.

Typeof in javascript has these behaviors:
```ts
const valueString = "string";
const valueNumber = 1;
const valueBoolean = true;
const valueBigInt = 1n;
const valueFunction = () => true;
const valueUndefined = undefined;
const valueNull = null;
const object = {
  prop1: "value1",
  prop2: "value2",
};

console.log(typeof valueString); // string
console.log(typeof valueNumber); // number
console.log(typeof valueBoolean); // boolean
console.log(typeof valueBigInt); // bigint
console.log(typeof valueFunction); // function
console.log(typeof valueUndefined); // undefined
console.log(typeof valueNull); // object
console.log(typeof object); // object
```
How we can see some things are strange: e.g. when we get the typeof of a null variable javascript returns an object type.

But here we see the same example in typescript:
```ts
type valueStringType = typeof valueString; // "string"
type valueNumberType = typeof valueNumber; // 1
type valueBooleanType = typeof valueBoolean; // true
type valueBigIntType = typeof valueBigInt; // 1n
type valueFunctionType = typeof valueFunction; // () => boolean
type valueUndefinedType = typeof valueUndefined; // undefined
type valueNullType = typeof valueNull; // null
type objectType = typeof object; // { prop1: string; prop2: string; }
```
The first impact is friendlier for us developers because the typeof operator converts the type exactly as expected. The best advantages can be seen in the types: function, null, object.

But now an advanced example:
```ts
const item = {
  id: '0000',
  name: 'Item',
  unit: {
    id: '1',
    code: 'PZ'
  },
  variants: [{
    id: '1',
    code: '001',
    color: 'FFFFFF'
  }]
};

type Item = typeof item;
type Unit = typeof item["unit"];
type Variant = typeof item.variants[number];
```
In this example, we can see how we can extract simple types from a complex object.

I leave you the [in this reference](https://www.typescriptlang.org/docs/handbook/2/typeof-types.html) of the official documentation of this operator.

For today is all.
See you soon!