Display a caution when verifying a function's value instead of its return value

Question

Display a caution when verifying a function's value instead of its return value

I've encountered a common pitfall (especially with autocomplete) while testing a function return value. There are instances when I forget to include the parentheses () at the end, causing it to always return true.

class Foo {
    public bar(): boolean {
        // Return true or false based on certain logic
    }
}

let foo = new Foo();
if (foo.bar) {
    // UNINTENDED
    // Always returns true because "foo.bar" is a function object
}

if (foo.bar()) {
    // INTENDED
    // Returns either true or false depending on the logic within "foo.bar"
}

Is there a way to receive notifications/warnings when using the former approach? During debugging, it's not always obvious that I missed the function call, making it challenging to identify the problem. Alternatively, are there better coding practices to prevent this issue?

As a user of VS Code, I am open to any linting tools or suggestions that can help alert me about this problem.

javascript typescript visual-studio-code

Answer 1

Answer №1

Considering that using bar as a property getter makes sense, it would be beneficial to redefine it as one. This way, Typescript can provide guidance on correct usage.

Locating the appropriate TSLint flag for your needs may prove challenging. For instance, employing if (obj.someFunction) { is common in Javascript for testing function invocation and is considered valid.

Converting it into a property getter is a straightforward task.

Example:

class test {
    get bar(): boolean {
        return true;
    }
}

var a = new test();

//This works fine.
if (a.bar) {}

//ERROR: Cannot invoke an expression whose type lacks a 
//call signature.
if (a.bar()) {}

Answer 2

Considering that using bar as a property getter makes sense, it would be beneficial to redefine it as one. This way, Typescript can provide guidance on correct usage.

Locating the appropriate TSLint flag for your needs may prove challenging. For instance, employing if (obj.someFunction) { is common in Javascript for testing function invocation and is considered valid.

Converting it into a property getter is a straightforward task.

Example:

class test {
    get bar(): boolean {
        return true;
    }
}

var a = new test();

//This works fine.
if (a.bar) {}

//ERROR: Cannot invoke an expression whose type lacks a 
//call signature.
if (a.bar()) {}

Answer 3

Answer №2

When considering ways to address this issue, a couple of solutions come to mind. One possibility is to utilize a linter tool such as TSLint with the strict-boolean-expressions option which may provide the desired outcome. Another approach could involve transforming the method in question into a getter function.

Answer 4

When considering ways to address this issue, a couple of solutions come to mind. One possibility is to utilize a linter tool such as TSLint with the strict-boolean-expressions option which may provide the desired outcome. Another approach could involve transforming the method in question into a getter function.

Display a caution when verifying a function's value instead of its return value

Answer №1

Answer №2

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