ts-issues.ts

// Bug 1
// Typescript only looks at the fields and methods to type check, not the constructors.
// Root cause: structural typing
class Animal {
    feet: number;
    constructor(name: string, numFeet: number) { }
}

class Size {
    feet: number;
    constructor(numFeet2: number) { }
}

let a: Animal = new Size(1); // You probably didn't mean to do that.



// Bug 2
// Typescript does not help me refactor this code
// Root cause: implicit type coercion in if condition
function doSomething(): boolean {
    return false;
}

if (doSomething()) { // all good!
    console.log(doSomething());
}

function doSomethingWrong(): Promise<boolean> {
    return new Promise((resolve) => resolve(false));
}

if (doSomethingWrong()) { // Oh no, bug! This is always true
    console.log(doSomethingWrong());
}


// Bug 3
// Typescript does no help me refactor this code.
// Root cause: implicit polymorphism of `+` operator
let getA = (): string => "first ";
let getB = (): string => "and second";

let doSomethingGeneric = () => getA() + getB();

let c = doSomethingGeneric(); // type string

let getB2 = (): number => 2;
let doSomethingGeneric2 = () => getA() + getB2();
let c2 = doSomethingGeneric2(); // type string


// Bug 4
// Typescript doesn't help me refactor this code.
// Root cause: does not enforce that statements return `unit` (nothing) type
let doSomethingCool = () => {
    return 1;
}

let main = () => {
    // do stuff ...
    doSomethingCool(); // everything is fine
    // do other stuff ...
};

let doSomethingCool2 = async () => {
    return await new Promise((resolve) => resolve(1));
};

let main2 = () => {
    // some code ...

    doSomethingCool2(); // Wrong, you should await, but not type error

    // some code ...
};


// Bug 5
// Typescript does not help me refactor this code
// Root cause: when running in the browser context, every property in `window` is available
let main3 = () => {
    let name = "Hey";
    // some code ...

    console.log(name); // everything is fine
};

let main4 = () => {
    // some code ...
    
    console.log(name); // Wrong because we wanted to remove the declaration of `name`.
};


// Bug 6

let x = () => ({name: "Alice"});
let y = () => ({name: "Alice", location: "Seattle"});

x = y; // OK
y = x; // Error

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