testing destructuring assignment `this` patterns

DestructuringThisTest.js

// By James M Snell @jasnell

// the first tweet:
// https://twitter.com/jasnell/status/1385464365046894599?s=20

class F {
    a = 1;
    b() {
        return this.a;
    }
}

const { b } = new F;
try {
    console.log(b());
} catch (error) {
    console.error(error);
}

// the second tweet
// https://twitter.com/jasnell/status/1385464988798648321

class E {
    a = 1;
    get c() {
        return () => {
            return this.a;
        }
    }
}

const { c } = new E;

console.log('c      :', c());
console.log('c.call :', c.call({ a: 2 }));


// preferred version then
// https://twitter.com/went_out/status/1385470268060180480


class G {
    a = 1;
    get d() {
        const me = this;
        return function () {
            return (this || me).a;
        }
    }
}

const { d } = new G;

console.log('d      :', d());               // 1
console.log('d.call :', d.call({ a: 2 }));  // 2


// and seems this might also mean something important
// https://twitter.com/jasnell/status/1385549464912289792?s=20

const handler = function () {
    const me = this;
    return function () {
        // we need strict here,
        // as otherwise this will be
        // a pointer to global!
        'use strict';
        const thisPointer = this || me;
        if (thisPointer instanceof H) {
            return thisPointer.a;
        }
        throw new TypeError('Value Access Denied!');
    }
}

class H {
    a = 1;
    get e() {
        return handler.call(this);
    }
}

const h = new H;
const { e } = h;

console.log('e      :', e());                       // 1

try {
    console.log('e.call 1st :');
    e.call({ a: 2 });
} catch (error) {
    console.error(error);
}

console.log('e.call 2nd :', e.call(h));             // 1


// step 5 : how do we do with multi inheritance!
class K {
    a = 1;
    get f() {
        return handler.call(this);
    }
}

const k = new K;
const { f } = k;

const multiProp = {
    a: 3,
    e,
    f,
};

console.log('multi prop example\n\n\n');

try {
    console.log('\nmultiProp.e');
    multiProp.e();
} catch (error) {
    console.log('as expected !');
    console.error(error);
}

try {
    console.log('\nmultiProp.f');
    multiProp.f();
} catch (error) {
    console.log('as expected !');
    console.error(error);
}

console.log('\n');

console.log('and obvious thurther destructuring re-assignment ↓↓↓\n');

const {
    e: x,
    f: y,
} = multiProp;

debugger;
console.log('sure console.log(x()) works!');
console.log('as x is prop from instance of H');
console.log(x());
console.log('as expected !');

try {
    console.log('\nbut y() does not!');
    console.log('\nas y is prop from instanceof K');
    debugger;
    y();
} catch (error) {
    console.log('!!!');
    console.error(error);
}