Javascript obje.key undefined when assigned to the object itself

Question

I watched a fragment from here

var foo = {n: 1};
var bar = foo;
foo.x = foo = {n: 2};

When I write foo.x it says undefined. Why is this so? I expected it to be {n: 2}

Answer 1

Values ​​are assigned from left to right, so this happens:

foo.x = {n: 2};

which leads to the fact that foo is {n: 1, x: {n: 2}}

then foo is assigned a new value

foo = {n: 2};

which overrides it on {n: 2}.

Answer 2

foo.x , x foo. 12.14.4 : (ES6, ), , ( ) ( ).

, :

var foo = {n: 1};
var bar = foo;
foo.x = foo = {n: 2};
console.log(foo, bar)

Hide result

var foo = {n: 1};
var bar = foo;
bar.x = foo = {n: 2};
console.log(foo, bar)

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var foo = {n: 1};
var bar = foo;
foo.x = (foo = {n: 2});
console.log(foo, bar)

Hide result