Tips for ensuring a method is not invoked more than once with identical arguments

Question

Tips for ensuring a method is not invoked more than once with identical arguments

I'm grappling with a challenge in JavaScript (or typescript) - ensuring that developers cannot call a method multiple times with the same argument.

For instance:

const foo = (name: string) => {}


foo("ABC") // ok

foo ("123") // ok

foo ("ABC") // ideally, should prompt an error in the IDE indicating that it was already called with the same value previously

To clarify, I am looking to catch this error during the development process, prior to runtime. My intention is for developers to be notified of any mistakes while coding, prompting the IDE to flag the error.

Is there a way to accomplish this? Perhaps through creating a custom tslint rule?

Edit: If achieving the desired outcome above is not natively supported in JavaScript, then alternatively, a new custom tslint rule could suffice. Rules have the capability to store values and context, which can potentially trigger errors during development time, similar to other linting rules in the IDE.

Is this achievable? How would one go about creating a new lint rule with contextual awareness to address this issue?

Furthermore, I am open to scenarios where foo(x) is utilized and the rule may not recognize the exact value of x or the order in which the function is invoked.

The rule only needs to be intelligent enough to handle basic cases where possible.

javascript typescript

Answer 1

Answer №1

One way to handle this issue is by throwing an error at runtime during development:

const usedNames = []

const foo = (name: string) => {
  if (process.env.NODE_ENV === 'development') {
    if (usedNames.includes(name)) throw new Error(`Function already called with ${ name }.`)

    usedNames.push(name)
  }

  ...
}

In non-development builds, the

if (process.env.NODE_ENV === 'development') { ... }

block will be omitted altogether. You can learn more about handling environment variables in webpack here.

Answer 2

One way to handle this issue is by throwing an error at runtime during development:

const usedNames = []

const foo = (name: string) => {
  if (process.env.NODE_ENV === 'development') {
    if (usedNames.includes(name)) throw new Error(`Function already called with ${ name }.`)

    usedNames.push(name)
  }

  ...
}

In non-development builds, the

if (process.env.NODE_ENV === 'development') { ... }

block will be omitted altogether. You can learn more about handling environment variables in webpack here.

Answer 3

Answer №2

Regrettably, neither TypeScript nor JavaScript have the capability to implement this type of feature natively. To my knowledge, there is no built-in mechanism in JavaScript or TypeScript that enables you to impose restrictions at compile-time based on runtime values or usage. These languages are simply not intended to track this kind of behavior.

Typically, a static type checker like TypeScript examines types through static analysis without actually executing or tracing the code. Therefore, TypeScript cannot perform checks that rely on the runtime behavior of the code, such as the sequence or frequency of function calls.

To identify these logical issues early on, unit tests are often a more effective option. You could create a test that verifies if 'foo' throws an error when called with the same argument twice, and then regularly run your tests during development. Another approach could be utilizing a linter or static analysis tool that supports custom rules, although I am unsure if any existing tools can handle this specific scenario.

If you wish to enforce such a rule, your best course of action may be to provide documentation or comments clarifying the requirement, and trust developers to adhere to it manually.

Additionally, it is possible that your situation could benefit from a different pattern or structure. If you frequently encounter the need to prevent developers from invoking a method multiple times with the same argument, it might be worth considering a design that preemptively eliminates that possibility altogether.

Answer 4

Regrettably, neither TypeScript nor JavaScript have the capability to implement this type of feature natively. To my knowledge, there is no built-in mechanism in JavaScript or TypeScript that enables you to impose restrictions at compile-time based on runtime values or usage. These languages are simply not intended to track this kind of behavior.

Typically, a static type checker like TypeScript examines types through static analysis without actually executing or tracing the code. Therefore, TypeScript cannot perform checks that rely on the runtime behavior of the code, such as the sequence or frequency of function calls.

To identify these logical issues early on, unit tests are often a more effective option. You could create a test that verifies if 'foo' throws an error when called with the same argument twice, and then regularly run your tests during development. Another approach could be utilizing a linter or static analysis tool that supports custom rules, although I am unsure if any existing tools can handle this specific scenario.

If you wish to enforce such a rule, your best course of action may be to provide documentation or comments clarifying the requirement, and trust developers to adhere to it manually.

Additionally, it is possible that your situation could benefit from a different pattern or structure. If you frequently encounter the need to prevent developers from invoking a method multiple times with the same argument, it might be worth considering a design that preemptively eliminates that possibility altogether.

Answer 5

Answer №3

You can utilize chaining to sequentially list the arguments that have been used
https://tsplay.dev/WJpZrN

type conform<T, V, E> = T extends V ? T : { error: E }

type Chain<T> = {
  foo<V extends string>(
    name: conform<V, Exclude<V, T>, 'this argument is already used'>,
  ): Chain<T | V>
}

function chain(fn: (s: string) => void): Chain<never> {
  const c = {
    foo(s: string) {
      fn(s);
      return c;
    }
  };
  return c as any;
}

chain(console.log)
.foo('a') // acceptable
.foo('b')
.foo('a')

let cc;
cc = chain(console.log)
cc = cc.foo('a'); // appropriate
cc = cc.foo('b')
cc = cc.foo('a')

Answer 6

You can utilize chaining to sequentially list the arguments that have been used
https://tsplay.dev/WJpZrN

type conform<T, V, E> = T extends V ? T : { error: E }

type Chain<T> = {
  foo<V extends string>(
    name: conform<V, Exclude<V, T>, 'this argument is already used'>,
  ): Chain<T | V>
}

function chain(fn: (s: string) => void): Chain<never> {
  const c = {
    foo(s: string) {
      fn(s);
      return c;
    }
  };
  return c as any;
}

chain(console.log)
.foo('a') // acceptable
.foo('b')
.foo('a')

let cc;
cc = chain(console.log)
cc = cc.foo('a'); // appropriate
cc = cc.foo('b')
cc = cc.foo('a')

Tips for ensuring a method is not invoked more than once with identical arguments

Answer №1

Answer №2

Answer №3

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