"Utilize Typescript to dynamically check data types during runtime and receive alerts for any potential

Question

"Utilize Typescript to dynamically check data types during runtime and receive alerts for any potential

INTRODUCTION

I am currently working with Angular 6.

In Angular, typescript is utilized to allow you to specify the data type of your function's arguments:

public fun1(aaa: number) {
  console.log(aaa);
}

If I attempt to call fun1 with a parameter of a different type, an error will be thrown:

public fun2() {
  this.fun1([1, 2, 3]); // TS2345: Argument of type 'number[]' is not assignable to parameter of type 'number'
}

THE PROBLEM

Type checking works effectively when I have control over the arguments in my code files.

However, there are situations where fun1 may be called with parameters retrieved from a backend source.

Since Typescript does not perform runtime checking, no errors would be shown and the code within fun1 would execute with the unexpected input like [1, 2, 3].

-- edited --

The issue isn't just limited to backend responses. In some cases, a library might alter the data type without your knowledge. For example, when using Reactive Forms with a control that should contain a number, it could inadvertently convert the value to a string during editing.

QUESTION

Is there a standard method for implementing type checking at runtime?

I've considered something along these lines:

public fun1(aaa: number) {
  if (typeof aaa !== 'number') {
    console.warn('wrong type');
  } else {
    console.log(aaa);
  }
}

, but WebStorm alerts me that

typeof check is always false: 'aaa' always has type 'number'

.

Including such checks at the beginning of every function seems cumbersome and unnecessary. Does anyone have a more efficient solution for this dilemma?

angular typescript

Answer 1

Answer №1

TypeScript was intentionally designed without providing runtime type information (refer to https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals, Non-goals, point 5).

When TypeScript interacts with external data sources, such as data attributes in HTML or data fetched from a REST API, it cannot determine the data type by itself. However, there are workarounds available. Let's explore two possible solutions.

One way is to bypass the type system using the `as` operator. While not completely type-safe (creating a hole in the type system), this approach aligns partially with TypeScript's objectives (referencing the link above).

For instance, if a function call like `fetchApiSync` returns a simple JavaScript object `{name: "John", age: 42}`, and we have a function:

function introduceMe(person: Person) {
    return `My name is ${person.name} and I'm ${person.age} years old.`
}

along with an interface

interface Person {
    name: string;
    age: number;
}

We can do the following:

const person: Person = fetchPersonFromApi(1);

.

It is ideal for `fetchPersonFromApi` to return a value that matches the `Person` interface so that we can further process it:

const introduction = introduceMe(person);

To achieve this, we might perform something like this:

function fetchPersonFromApi(id: number): Person {
   // synchronous call without error handling for simplicity
   const response: Person = fetchApiSync(`/persons/${id}`) as Person

   return response;
}

This code snippet includes an explicit cast of the API response to a `Person`, ensuring type checking. However, issues may arise if a different data type is returned instead of `Person`. Is there a solution to this problem?

Alternatively, one can utilize `any` (or `unknown` from TS 3) types, allowing skipping of strict type checks where a value of type `any` can be assigned to any other type, including `Person`. Yet, errors may become challenging to debug within the type system. Thus, caution is advised when using these types!

Another viable option is leveraging the `io-ts` library (https://github.com/gcanti/io-ts). This library enables the specification of `runtime types` and conducting runtime type validations, adding an overhead to ensure values match expected types. While introducing additional complexity, io-ts promotes increased type safety and discourages resorting to `any` or `unknown` types. It facilitates deriving pure TypeScript types from io-ts definitions, safeguarding the codebase against reckless type conversions. However, mastering io-ts entails embracing and managing its inherent complexities effectively.

Answer 2

TypeScript was intentionally designed without providing runtime type information (refer to https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals, Non-goals, point 5).

When TypeScript interacts with external data sources, such as data attributes in HTML or data fetched from a REST API, it cannot determine the data type by itself. However, there are workarounds available. Let's explore two possible solutions.

One way is to bypass the type system using the `as` operator. While not completely type-safe (creating a hole in the type system), this approach aligns partially with TypeScript's objectives (referencing the link above).

For instance, if a function call like `fetchApiSync` returns a simple JavaScript object `{name: "John", age: 42}`, and we have a function:

function introduceMe(person: Person) {
    return `My name is ${person.name} and I'm ${person.age} years old.`
}

along with an interface

interface Person {
    name: string;
    age: number;
}

We can do the following:

const person: Person = fetchPersonFromApi(1);

.

It is ideal for `fetchPersonFromApi` to return a value that matches the `Person` interface so that we can further process it:

const introduction = introduceMe(person);

To achieve this, we might perform something like this:

function fetchPersonFromApi(id: number): Person {
   // synchronous call without error handling for simplicity
   const response: Person = fetchApiSync(`/persons/${id}`) as Person

   return response;
}

This code snippet includes an explicit cast of the API response to a `Person`, ensuring type checking. However, issues may arise if a different data type is returned instead of `Person`. Is there a solution to this problem?

Alternatively, one can utilize `any` (or `unknown` from TS 3) types, allowing skipping of strict type checks where a value of type `any` can be assigned to any other type, including `Person`. Yet, errors may become challenging to debug within the type system. Thus, caution is advised when using these types!

Another viable option is leveraging the `io-ts` library (https://github.com/gcanti/io-ts). This library enables the specification of `runtime types` and conducting runtime type validations, adding an overhead to ensure values match expected types. While introducing additional complexity, io-ts promotes increased type safety and discourages resorting to `any` or `unknown` types. It facilitates deriving pure TypeScript types from io-ts definitions, safeguarding the codebase against reckless type conversions. However, mastering io-ts entails embracing and managing its inherent complexities effectively.

"Utilize Typescript to dynamically check data types during runtime and receive alerts for any potential

Answer №1

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