The type 'true | CallableFunction' does not have any callable constituents

Question

The type 'true | CallableFunction' does not have any callable constituents

The error message in full:

This expression is not callable.
  No constituent of type 'true | CallableFunction' is callable

Here is the portion of code causing the error:

public static base(
    text,
    callB: boolean | CallableFunction = false,
    
  ) {
    const sw = Swal.fire({
      text,
      });

    if (callB) {
      sw.then(callB());
    }
  }

To address the issue, I updated the type of callB to :

 callB: (param: any) => void |boolean = false

However, upon removing the callB type definition:

callB= false

A new error emerged:

This expression is not callable.
  Type 'Boolean' has no call signatures

javascript typescript

Answer 1

Answer №1

Here is the solution you've been seeking:

function base(text: string, callB: false | CallableFunction = false) {
  console.log(text);
  if (callB) {
    callB();
  }
}

The main idea is to pass a function or false. If the value is truthy, the function should be called.

However, based on your specifications

function base(text: string, callB: boolean | CallableFunction = false) {
  console.log(text);
  if (callB) {
    callB();
  }
}

This sample call would work: base('some str', true) where callB is true and not a function that will be executed using callB(). A non-callable function cannot be executed, right? Hence the error.

Check out the TypeScript Playground link for more details: https://tsplay.dev/m056qW

Answer 2

Here is the solution you've been seeking:

function base(text: string, callB: false | CallableFunction = false) {
  console.log(text);
  if (callB) {
    callB();
  }
}

The main idea is to pass a function or false. If the value is truthy, the function should be called.

However, based on your specifications

function base(text: string, callB: boolean | CallableFunction = false) {
  console.log(text);
  if (callB) {
    callB();
  }
}

This sample call would work: base('some str', true) where callB is true and not a function that will be executed using callB(). A non-callable function cannot be executed, right? Hence the error.

Check out the TypeScript Playground link for more details: https://tsplay.dev/m056qW

Answer 3

Answer №2

When dealing with the type

boolean | Function

it essentially translates to

true | false | Function

Since a value of type Function is considered truthy, the following check

if (callB)

limits the type of callB to

true | Function

and considering that true cannot be called, it results in an error.

If you are unsure about how to utilize your base method, here are two potential solutions:

If accepting true is not appropriate, modify your parameter type accordingly

static base(
    text, 
    callB: false | CallableFunction = false
) {
    if (callB) {
        callB();
    }
}

If handling true is necessary, employ a more precise conditional statement like

if (typeof callB === 'function') {
    callB() // It will work fine
}

Answer 4

When dealing with the type

boolean | Function

it essentially translates to

true | false | Function

Since a value of type Function is considered truthy, the following check

if (callB)

limits the type of callB to

true | Function

and considering that true cannot be called, it results in an error.

If you are unsure about how to utilize your base method, here are two potential solutions:

If accepting true is not appropriate, modify your parameter type accordingly

static base(
    text, 
    callB: false | CallableFunction = false
) {
    if (callB) {
        callB();
    }
}

If handling true is necessary, employ a more precise conditional statement like

if (typeof callB === 'function') {
    callB() // It will work fine
}

Answer 5

Answer №3

When utilizing the combination of false | Callablefunction (or boolean | CallableFunction), it is possible to force a type conversion by employing the typeof operator:

static base(
    text,
    callB: false | CallableFunction = false
) {
    if (typeof callB === "function") {
        callB()
    }
}

Answer 6

When utilizing the combination of false | Callablefunction (or boolean | CallableFunction), it is possible to force a type conversion by employing the typeof operator:

static base(
    text,
    callB: false | CallableFunction = false
) {
    if (typeof callB === "function") {
        callB()
    }
}

The type 'true | CallableFunction' does not have any callable constituents

Answer №1

Answer №2

Answer №3

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