Is it considered poor practice in TypeScript to manually set the type when the type inference is already accurate?

Is it necessary to explicitly set the variable type in TypeScript when it is inferred correctly? For example:

const add = (a: number, b: number) => a + b;

const result = add(2, 3);

// Or should I explicitly declare the return value type?
const add = (a: number, b: number): number => a + b;

const result = add(2, 3);

I understand that type inference covers many scenarios. If not considered bad practice, are there any instances where explicit types are preferred?

Answer №1

When considering the suitable moment to include explicit types in code, it is important to acknowledge that this decision can vary based on personal preferences. While not mandatory in cases where type inference is possible, there are both advantages and disadvantages to implementing explicit types:

Downsides:

  • Introducing explicit types requires additional effort and increases the amount of code, consequently adding maintenance costs.

Upsides:

  • Explicit types improve code readability by clearly indicating the intended return type of a function. They also serve as a quick reference for understanding the maintained type without relying on advanced IDE features like TSC.
  • Utilizing explicit types helps prevent bugs in function implementation by enforcing the declared return type and ensuring consistency throughout the codebase. This practice safeguards against inadvertent changes to the return type during code modifications.

In my opinion, while simple functions may not necessitate explicit types (such as basic lambda functions with a single return value), they are immensely beneficial for complex functions with multiple return statements. Given that functions tend to grow in complexity over time, I lean towards incorporating explicit return types in functions for long-term maintainability.

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