Input values that are true, or in other words, fulfill conditions for truthiness

Question

Input values that are true, or in other words, fulfill conditions for truthiness

Is there a specific data type in TypeScript to represent truthy values?

Here's the method I'm working with:

Object.keys(lck.lockholders).length;
    enqueue(k: any, obj?: any): void

It seems like TypeScript allows checking for empty strings '', but I'm unsure how to define a type for Truthy.

I want to modify it to:

    enqueue(k: Truthy, obj?: any): void

However, I am struggling to determine what type should be assigned to Truthy.

The main motivation behind this change is to prevent users from passing in null, undefined, or '' as keys to a hash.

typescript tsc truthy

Answer 1

Answer №1

Curiosity piqued, you may be wondering why this is necessary. To put it simply, TypeScript may not be the ideal choice for such a task. Runtime checks coupled with thorough code documentation could serve as a more effective solution to ensure developers understand the necessity of a truthy parameter like k. However, if you're adamant about making TypeScript work in this scenario, read on:

Note: Enabling the strictNullChecks compiler option is crucial. Without it, distinguishing between Truthy and Truthy | null | undefined would present a major issue.

You can define a pseudo-falsy type nearly resembling:

type Falsy = false | 0 | "" | null | undefined

It's important to note that even though Falsy is defined above, there are no negated types in TypeScript. Therefore, expressing Truthy as "everything except Falsy" proves challenging.

One potential approach involves utilizing conditional types to exclude potentially falsy parameters in enqueue(), albeit unconventional:

// Conditional types implementation

This method prevents values that might be considered falsy from being passed, aligning with your objective. Yet, determining the actual intent remains ambiguous.

Update

After reviewing your revised question clarifying the need for the k parameter to exclusively accept a string (or possibly a

symbol</code), while also excluding only the empty string <code>""

, you could simplify the previous logic to:

// Simplified logic

Despite these optimizations, an issue arises when passing a general string to enqueue(), which could be essential for developers if the k value isn't a predetermined string literal:

// General string dilemma

To address this, creating a nominal type paired with a user-defined type guard could help validate a string's non-empty nature:

// Nominal type and type guard example

This allows developers to confidently utilize strings within the constraints of the checker function. It does involve some complexity, so consider its value based on your specific needs. Best of luck!

Answer 2

Curiosity piqued, you may be wondering why this is necessary. To put it simply, TypeScript may not be the ideal choice for such a task. Runtime checks coupled with thorough code documentation could serve as a more effective solution to ensure developers understand the necessity of a truthy parameter like k. However, if you're adamant about making TypeScript work in this scenario, read on:

Note: Enabling the strictNullChecks compiler option is crucial. Without it, distinguishing between Truthy and Truthy | null | undefined would present a major issue.

You can define a pseudo-falsy type nearly resembling:

type Falsy = false | 0 | "" | null | undefined

It's important to note that even though Falsy is defined above, there are no negated types in TypeScript. Therefore, expressing Truthy as "everything except Falsy" proves challenging.

One potential approach involves utilizing conditional types to exclude potentially falsy parameters in enqueue(), albeit unconventional:

// Conditional types implementation

This method prevents values that might be considered falsy from being passed, aligning with your objective. Yet, determining the actual intent remains ambiguous.

Update

After reviewing your revised question clarifying the need for the k parameter to exclusively accept a string (or possibly a

symbol</code), while also excluding only the empty string <code>""

, you could simplify the previous logic to:

// Simplified logic

Despite these optimizations, an issue arises when passing a general string to enqueue(), which could be essential for developers if the k value isn't a predetermined string literal:

// General string dilemma

To address this, creating a nominal type paired with a user-defined type guard could help validate a string's non-empty nature:

// Nominal type and type guard example

This allows developers to confidently utilize strings within the constraints of the checker function. It does involve some complexity, so consider its value based on your specific needs. Best of luck!

Answer 3

Answer №2

While there isn't a specific Truthy type, you can make use of the type guard system to assist TypeScript in determining what qualifies as truthy and assigning it the appropriate type!

Let's establish the Falsy type and create a generic function named isTruthy:

type Falsy = false | 0 | '' | null | undefined;

// this serves as a type predicate - if x is deemed `truthy`, then it's T
const isTruthy = <T>(x: T | Falsy): x is T => !!x;

With our isTruthy function, we can identify Truthy values and have TypeScript appropriately assign the "truthy" type to the outcome.

Examples:

{   // eliminating boolean "false" type
  const result: string | false = Math.random() > 0.5 ? 'a' : false;
  const truthyResult: string = isTruthy(result) ? result : 'was false';
}
{   // extracting only numbers from an array
  const result: (number | undefined)[] = [42, undefined, 8, 16];
  const truthyResult: number[] = result.filter(isTruthy);
}
{   // extracting only Promises from an array
  const result: (Promise<string> | null)[] = [Promise.resolve('a'), null, Promise.resolve('b'), Promise.resolve('c')];
  const truthyResult: Promise<string>[] = result.filter(isTruthy);
}

Answer 4

While there isn't a specific Truthy type, you can make use of the type guard system to assist TypeScript in determining what qualifies as truthy and assigning it the appropriate type!

Let's establish the Falsy type and create a generic function named isTruthy:

type Falsy = false | 0 | '' | null | undefined;

// this serves as a type predicate - if x is deemed `truthy`, then it's T
const isTruthy = <T>(x: T | Falsy): x is T => !!x;

With our isTruthy function, we can identify Truthy values and have TypeScript appropriately assign the "truthy" type to the outcome.

Examples:

{   // eliminating boolean "false" type
  const result: string | false = Math.random() > 0.5 ? 'a' : false;
  const truthyResult: string = isTruthy(result) ? result : 'was false';
}
{   // extracting only numbers from an array
  const result: (number | undefined)[] = [42, undefined, 8, 16];
  const truthyResult: number[] = result.filter(isTruthy);
}
{   // extracting only Promises from an array
  const result: (Promise<string> | null)[] = [Promise.resolve('a'), null, Promise.resolve('b'), Promise.resolve('c')];
  const truthyResult: Promise<string>[] = result.filter(isTruthy);
}

Answer 5

Answer №3

As someone who may not be an expert in TypeScript, I have found success with version 4.8.2 using the following code:

type Falsy = null | undefined | false | 0 | -0 | 0n | '';

type Truthy<T> = T extends Falsy ? never : T;

While I may struggle to explain it thoroughly, here is an example for reference:

type MaybeUndefinedObject = object | undefined;

// Works
const truthyType: Truthy<MaybeUndefinedObject> = {};

// Fails with "Type 'undefined' is not assignable to type 'object'."
const truthyValue: Truthy<MaybeUndefinedObject> = undefined;

I hope this information proves useful. Feel free to let me know if it falls short of expectations.

Answer 6

As someone who may not be an expert in TypeScript, I have found success with version 4.8.2 using the following code:

type Falsy = null | undefined | false | 0 | -0 | 0n | '';

type Truthy<T> = T extends Falsy ? never : T;

While I may struggle to explain it thoroughly, here is an example for reference:

type MaybeUndefinedObject = object | undefined;

// Works
const truthyType: Truthy<MaybeUndefinedObject> = {};

// Fails with "Type 'undefined' is not assignable to type 'object'."
const truthyValue: Truthy<MaybeUndefinedObject> = undefined;

I hope this information proves useful. Feel free to let me know if it falls short of expectations.

Input values that are true, or in other words, fulfill conditions for truthiness

Answer №1

Update

Answer №2

Answer №3

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