typescript-extends-builtin-array

test.ts

// BAD
class A extends Array {
    constructor(array: number[]) {
        super();
        console.log(array); // called twice with other array 1st => [1, 2, 3], 2nd(not an array type) => 3
        array.forEach((a, i) => this[i] = a); // => Uncaught TypeError: array.forEach is not a function
    }
}

const a = new A([1,2,3]);

a.map(b => {
    console.log(b);
})

// OK
class A extends Array {
    static fromArray(arr: number[]): A {
        const c = new A();
        arr.forEach((a, i) => c[i] = a);
        return c;
    }
}

const a = A.fromArray([1,2,3]);

a.map(b => {
    console.log(b);
})