# Typescript - Tips & Tricks - Overloaded Functions

> Welcome back, guys! The topic of today is Overloaded Functions. All self-respecting programming...

- **Author**: Luca Del Puppo (@puppo92) — AI Native Engineer at Nearform
- **Published**: Feb 24, 2021
- **Canonical URL**: https://delpuppo.net/blog/ts-tips-and-tricks/typescript-tips-tricks-overloaded-functions/
- **Series**: TypeScript - Tips & Tricks (Part 5 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-overloaded-functions
- **Dev.to Mirror**: https://dev.to/playfulprogramming/typescript-tips-tricks-overloaded-functions-f75
- **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/) **(Current Article)**
- 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/)

---

Welcome back, guys!
The topic of today is [Overloaded Functions](https://www.typescriptlang.org/docs/handbook/declaration-files/by-example.html#overloaded-functions).

All self-respecting programming languages ​​have overloaded functions, so typescript has this feature too.
To use this feature in typescript, we have to declare all the signatures of this function, and at the end, we have to write a single function that includes all these signatures. The last function is the only one with the implementation. The peculiarity of this function is that it must include all the possible implementations of the previous signatures.
Here's a simple example that is more exhaustive than all these words.
```ts
function reverse(value: string): string;
function reverse(value: string[]): string[];
function reverse(value: string | string[]): string | string[] {
  if (typeof value === "string") return value.split("").reverse().join("");

  return value.slice().reverse();
}

console.log(reverse("Tips")); // 'spiT'
console.log(reverse(["T", "i", "p", "s"])); // [ 's', 'p', 'i', 'T' ]
```
As we can see, there are 2 signatures of the "reverse" function, one gets a string and returns a string as result, the second one gets a string array and returns a string array as result. The third function is the real implementation of this function. As we can see the parameter type is a literal-type that includes a string or a string array (the combination of the type in the signatures' parameters), we can make the same considerations for the result's type.
In the function implementations, we detect the parameter's type at runtime and manipulate the parameter to return the correct type according to the function we are overloading.

An important thing to remember is that the implementation function is not exposed.

That's all for today!
See you soon guys!