The variable 'zeroValue' is missing an initial value and is not explicitly assigned in the constructor

I'm currently diving into typescript and came across this piece of code that involves Generics (Generic classes) in the TypeScript documentation. Can anyone spot the issue here?

class GenericNumber 
{ 
    zeroValue: T; 
    add: (x: T, y: T) => T; 
}

let myGenericNumber = new GenericNumber(); 
myGenericNumber.zeroValue = 0; 
myGenericNumber.add = function(x, y) 
{ 
    return x + y; 
};

Error: Property 'zeroValue' has no initializer and is not definitely assigned in the constructor.ts(2564)

Answer №1

One effective method for sharing your TypeScript code is by releasing it on the TypeScript playground.

It appears that you are referring to this specific example.

// It's crucial to include a generic initializer
class GenericNumber<T> {
// The TypeScript compiler will throw an error if you only define the type of the
// class property without initializing it
    zeroValue: T; 

    add: (x: T, y: T) => T;
}

let myGenericNumber = new GenericNumber<number>(); // Make sure to provide a generic initializer
myGenericNumber.zeroValue = 0;
myGenericNumber.add = function (x, y) {
    return x + y; // No errors will occur
};

Functional demo

class GenericNumber<T> {
// To address the error, consider defining a constructor 
// that accepts [zeroValue] and [add] as parameters
    constructor(public zeroValue: T, public add: (x: T, y: T) => T){
        this.zeroValue = zeroValue;
        this.add = add;
    }
}
const zeroValue = 0;
let myGenericNumber = new GenericNumber<number>(zeroValue, (a,b)=>a+b);
const result = myGenericNumber.add(40,2) // Output: 42

Ensure that your function does not interact with this, as this may require additional handling.

Answer №2

If you want to turn off these typescript features, there are a few different ways to do so.

For those using the TypeScript playground, navigate to the TS Config section and deselect the option for strictPropertyInitialization.

If your project involves the use of typescript, simply go into the tsconfig.json file and set

"strictPropertyInitialization": false
to disable this specific feature.

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