# Typescript - Tips & Tricks - Non-null assertion operator

> In some cases, you have a field that you initialize in a method, and if you follow the flow of the...

- **Author**: Luca Del Puppo (@puppo92) — AI Native Engineer at Nearform
- **Published**: Mar 15, 2021
- **Canonical URL**: https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-non-null-assertion-operator/
- **Series**: TypeScript - Tips & Tricks (Part 13 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-non-null-assertion-operator
- **Dev.to Mirror**: https://dev.to/playfulprogramming/typescript-tips-tricks-non-null-assertion-operator-21eb
- **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/)
- 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/) **(Current Article)**
- 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/)

---

In some cases, you have a field that you initialize in a method, and if you follow the flow of the code you are sure that this field is initialized but typescript doesn't understand it.
An example
```ts
type Person = {
  name: string;
};

let person: Person;

function initialize() {
  person = { name: "name" };
}

initialize();
console.log("Hello", person.name); // Variable 'person' is used before being assigned.
```
In this case, you can see how the typescript compiler doesn't understand that the "person" field isn't null but it's initialized.
To resolve this problem, the typescript language exposes us the _"Non-null assertion operation"_(!). This operator says to the compiler that the field isn't null or undefined but it's defined.
The previous example can be reviewed in this way
```ts
type Person = {
  name: string;
};

let person: Person;

function initialize() {
  person = { name: "name" };
}

initialize();
console.log("Hello", person!.name);
```
As you can see, in this case, the code doesn't have errors and the compilation ends with success.

That's all for today!
Bye-bye guys!