Javascript Object.assign行为异常

Question

In the following Javascript, the result is that it displays 1, 2, 3. I would expect it to display: 1, 2, 2. My understanding was that Object.assign would copy the values in an object.

 var myobj = { mynum: 1, mystr: "test", mydata: 6 } alert(myobj.mynum); let secondobj = myobj; secondobj.mynum = 2; alert(myobj.mynum); let thirdobj = Object.assign(myobj); thirdobj.mynum = 3; alert(myobj.mynum); 

Answer 1

It is the same object

var foo = {}
var bar = Object.assign(foo)
console.log(foo === bar) // true

To copy object values use

var bar = Object.assign({}, foo)

or spread operator (new in ECMAScript 2018)

var bar = { ...foo };

For your case

let thirdobj = Object.assign({}, myobj);

Answer 2

The definition is Object.assign(target, source)

So, this would work:

var myobj = {mynum: 1, mystr: "test", mydata: 6}
alert(myobj.mynum);

let secondobj = myobj;
secondobj.mynum = 2;
alert(myobj.mynum);

let thirdobj = {};
Object.assign(thirdobj, myobj);
thirdobj.mynum = 3;
alert(myobj.mynum);

You could also use:

let thirdobj = { ... myobj};
thirdobj.mynum = 3;
alert(myobj.mynum);

for brevity