Why inheriting from Array not working in TypeScript?

Question

I tried to inherit from Array, but the instanceof not working.

class MyList<T> extends Array<T> {}

const l = new MyList<string>()
console.log(l instanceof MyList)  // false <- WRONG
console.log(l instanceof Array)   // true

Possible duplicate of Why instanceof returns false for a child object in Javascript — jcalz
– jcalz, Commented Mar 19, 2019 at 17:17

Alex Craft · Accepted Answer · 2019-03-19 17:17:23Z

0

Thanks to @jcalz the code should be as below, more details

class MyList<T> extends Array<T> {
    constructor() {
        super()
        Object.setPrototypeOf(this, MyList.prototype)
    }

}
const l = new MyList<string>()
console.log(l instanceof MyList)  // false <- WRONG
console.log(l instanceof Array)   // true

answered Mar 19, 2019 at 17:17

Alex Craft

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