Classes

index.js

class Bem {

}

// src/common/Block/Block.js
class Block extends Bem {
    constructor() {
        super();
        this.a = 1;
    }

    tag() {
        return 'a';
    }
}

// src/common/Block/_mod/Block_mod_val1.js
class BlockModVal1Common extends Bem {
    constructor() {
        super();
        console.log(this.a); // 1
    }

    tag() {
        return 'b';
    }
}

// src/desktop/Block/_mod/Block_mod_val1.js
class BlockModVal1Desktop extends BlockModVal1Common {
    constructor() {
        super();
        this.a += 1;
        console.log(this.a); // 2
    }

    tag() {
        return 'bb';
    }
}

// src/common/Block/_mod/Block_mod_val2.js
class BlockModVal2Common extends Bem {
    constructor() {
        super();
        this.a += 1;
        console.log(this.a); // 2 or 3
    }

    tag() {
        return 'c' + super.tag(); // ca or cbb
    }
}

// ЭТО ВОТ МУТАБЕЛЬНО! ЛОМАЕТ СУЩЕСТВУЮЩИЕ ПРОТОТИПЫ!
function inherits(Inherited, Super) {
    Inherited.super_ = Super;
    Object.setPrototypeOf(Inherited.prototype, Super.prototype);
    return Object.setPrototypeOf(Inherited, Super);
}

const compose = (...mixins) => {
    const Base = mixins.splice(0, 1)[0];
    return mixins.reduce((Middle, Mixin) => {
        return inherits(Mixin, Middle);
    }, Base);
}
const Res4 = compose(Block, BlockModVal1Desktop, BlockModVal2Common);
const Res5 = compose(Block, BlockModVal1Desktop);
// const Res6 = compose(Block, BlockModVal1Common, BlockModVal2Common);


const inst4 = new Res4();
console.log('Composed: A, BB, C', inst4.tag(), inst4.a); // cbb, 3

const inst5 = new Res5();
console.log('Composed: A, BB', inst5.tag(), inst5.a); // bb, 2