使用对象分配添加键/值对失败

Question

I have an object that i am storing in local storage. I would like to retrieve the object and add an key/value item to it. This is the code

 var testObject = { 'one': 1, 'two': 2, 'three': 3 };

// Put the object into storage
localStorage.setItem('testObject', JSON.stringify(testObject));

// Retrieve the object from storage
var retrievedObject = localStorage.getItem('testObject');

var newdata = JSON.parse(retrievedObject);
var obj2 = {"four":"4"};
Object.assign(newdata, obj2);

$.each(JSON.parse(retrievedObject), function (index, value) {
  console.log(index+"  "+value);
});

The new item is not added to testObject . How can I add the item to the existing object?.

Answer 1

You are successfully changing newdata but then you do not use it. Instead you are calling JSON.parse(retrievedObject) again.

 var testObject = { 'one': 1, 'two': 2, 'three': 3 }; // Put the object into storage // Just use a variable because we cant use localstorage on snippet var storage = JSON.stringify(testObject); // Retrieve the object from storage var retrievedObject = storage; var newdata = JSON.parse(retrievedObject); var obj2 = {"four":"4"}; Object.assign(newdata, obj2); $.each(newdata, function (index, value) { console.log(index+" "+value); }); 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> 

Answer 2

retrievedObject is a string. You parse the string, modify the resulting object ( newdata gets modified). You should not expect the initial string to change.

In order to update localStorage, just do:

localStorage.setItem('testObject', JSON.stringify(newdata));

Note that after that operation retrievedObject would still be the string with { 'one': 1, 'two': 2, 'three': 3 }