Multiple assignment confusion

Question

I understand that the assignment operator is right associative.

So for example x = y = z = 2 is equivalent to (x = (y = (z = 2)))

Answer 1

Edited the answer to make it simple

First of all you have to understand the differnce between Reference- and Value- Type.

var foo = {};

foo variable holds a Reference to an object in memory, lets say A

Now, there are two arts of accessors: Variable Accessor and Property Accessor.

So foo.x = foo = {a:1} can be understood as

[foo_VARIABLE_ACCESSOR][x_PROPERTY_ACCESSOR] = [foo_VARIABLE_ACCESSOR] = {a:1}

!!! Accessor chain is evaluated first to get the last accessor, which is then evaluated associative.

A['x'] = foo = {a:1}

Property Accessor are seperated into setters and getters

var foo = { bar: {} };
foo.bar.x = foo = {a:1}

Here where have decared two nested objects foo and bar. In memory we have then two object A and B.

[foo_VAR_ACCESSOR][bar_PROP_GETTER][x_PROP_ACCESSOR] = [foo_VAR_ACCESSOR] = {a:1}

> A[bar_PROP_GETTER][x_PROP_ACCESSOR] = [foo_VAR_ACCESSOR] = {a:1}
> B[x_PROP_ACCESSOR] = [foo_VAR_ACCESSOR] = {a:1}
> B['x'] = foo = {a: 1}

Here you have little example

var A = {};
var B = {}
Object.defineProperty(A, 'bar', {
    get () {
        console.log('A.bar::getter')
        return B;
    }
})
Object.defineProperty(B, 'x', {
    set () {
        console.log('B.x::getter')
    }
});

var foo = A;
foo.bar.x = foo = (console.log('test'), 'hello');

// > A.bar.getter
// > test
// > B.x.setter