如何在Javascript中通过点运算符访问对象的属性

Question

var changeJsonKeyName, newObj, obj;
changeJsonKeyName = function(json, oldName, newName) {
  json[newName] = json[oldName];
  delete json[oldName];
//    json.newName = json.oldName;
//    delete json.oldName;
    // if i use point in this ,i  can not get my result that i want   


  return json;
};
obj = {
  'aaa': '1111',
  'bb': {
    'cc': 333
  }
};
newObj = {};
newObj = changeJsonKeyName(obj, 'aaa', 'nnn');
console.log(newObj);

If I use point here ,I can not get my result that's what I want ,what is the wrong,please help me,thank you very much.

Answer 1

I'm not sure if I understood you correctly, but :

json[newName]

access property named with the value of newName variable

json.newName

access a property named 'newName', which does not exist

Answer 2

First, as a comment points out, this is a Javascript question, not a JSON question.

But you seem to be asking why this works:

 json[newName] = json[oldName];
 delete json[oldName];

but this doesn't:

 json.newName. = json.oldName.;
 delete json.oldName;

does not.

And the answer is the second form is actually equivalent to

 json["newName"] = json["oldName"];
 delete json["oldName"];

In other words, you are dealing with attributes whose names are the constants "oldName" and "newName" rather than attributes whose names are passed as parameters to that method.