Javascript object 文字分配和参考如何工作？

Question

I have a simple question

let obj1 = {};
obj2= obj1;`

Here obj1 and obj2 are referencing the same object in the memory ie obj1===obj2 --> true . So by this logic any operation on obj2 will affect obj1.

Now if I assign a property to obj2

 let obj1 = {}; obj2 = obj1; obj2['a'] = {}; obj2 = obj2['a']; // why this operation didn't change obj1, if they are referencing the same object? console.log(obj1); // -- > { a: {} }; console.log(obj2); // -- > {};

now obj1===obj2 --> false why is this?

Also How come obj2 = {} is different then obj2 = obj2['a'] ?

A screenshot for clarifying myself

Thanks for your help in advance.

Answer 1

For objects, the assignment operator = assigns a reference to the object.

So in:

let obj1 = {};
let obj2 = obj1;

both obj1 and obj2 reference the same object. Now:

obj2['a'] = {};

creates a new property a and assigns it a value that is a reference to a new object. Since both obj1 and obj2 reference the same object, you'll also find:

obj2.a === obj1.a

But then:

obj2 = obj2['a']; // why this operation didn't change obj1, if they are referencing the same object ?

You've now assigned a different object to obj2 , so it now references the new object initially assigned to obj2.a and:

obj1.a === obj2;

So obj1 was modified (or more correctly, the object referenced by obj1 was modified).

Some code:

 // obj1 and obj2 reference the same object let obj1 = {}; let obj2 = obj1; console.log('obj2 === obj1 ' + (obj2 === obj1)); // true // Assign new object to obj2.a obj2['a'] = {}; // Affects obj1 console.log('obj2.a === obj1.a ' + (obj2.a === obj1.a)); // true // Assign new object to obj2 obj2 = obj2['a']; // obj2 now references a different object to obj1 console.log('obj1 === obj2 ' + (obj1 === obj2)); // false // obj1.a still references new object console.log('obj1.a === obj2 ' + (obj1.a === obj2)); // true

Answer 2

obj2 is an object, obj2[a] is another object. The result of comparing two objects is false.

 {} === {}    // false