Change key name in JavaScript object

Question

I am checking the attributes in a JavaScript object, replacing some of the keys by deleting the prefix \"element\" and saving the new values in another object.

Answer 1

The problem is that you are looking for the property in the original object using the new key. Use keys[j] instead of key:

var keys = Object.keys(json);
for (var j=0; j < keys.length; j++) {
   var key = keys[j].replace(/^element_/, "");
   tmp[key] = json[keys[j]];
}

I uses a regular expression in the replace so that ^ can match the beginning of the string. That way it only replaces the string when it is a prefix, and doesn't turn for example noexample_data into no_data.

Note: What you have is not "a json", it's a JavaScript object. JSON is a text format for representing data.

Is that due to the fact that I converted the keys (Objects) to Strings (with the replace method)?

No. The keys are strings, not objects.

---

You could also change the properties in the original object by deleting the old ones and adding new:

var keys = Object.keys(json);
for (var j=0; j < keys.length; j++) {
   if (keys[j].indexOf("element_") == 0) {
     json[keys[j].substr(8)] = json[keys[j]];
     delete json[keys[j]];
   }
}

Answer 2

We'll write a little function to fix the key the way you want.

function fix_key(key) { return key.replace(/^element_/, ''); }

Underscore

_.object(
  _.map(_.keys(json), fix_key),
  _.values(json)
)

ES5/loop

var keys = Object.keys(json);
var result = {};

for (i = 0; i < keys.length; i++) {
  var key = keys[i];
  result[fix_key(key)] = json[key];
}

return result;

ES5/reduce

Object.keys(json) . reduce(function(result, key) {
  result[fix_key(key)] = json[key];
  return result;
}, {});

ES6

Object.assign(
  {},
  ...Object.keys(json) .
    map(key => ({[fix_key(key)]: json[key]}))
)

This makes an array of little objects each with one key-value pair, using the ES6 "computed property name" feature, then passes them to Object.assign using the ES6 "spread" operator, which merges them together.

Answer 3

key is not original json because you have remove element_ prefix

var keys = Object.keys(json);
for (var j=0; j < keys.length; j++) {
   key = keys[j].replace("element_", "");
   var _key = keys[j];
   switch(key) {
   default :
      tmp[key] = json[_key];
      break;
   }
}

Answer 4

Try this:

var keys = Object.keys(json);
for (var j=0; j < keys.length; j++) {
   var key = keys[j]; // key
   var value = json[key]; // data
   delete json[key]; // deleting data with old key
   key = key.replace("element_", ""); // renaming key
   json[key] = value; // setting data with new key
}

or extend prototype of Object

Object.prototype.renameKey = function (oldName, newName) {
    if (!newName) return this;
    if (oldName === newName) return this;

    if (this.hasOwnProperty(oldName)) {
        this[newName] = this[oldName];
        delete this[oldName];
    }
    return this;
};

var keys = Object.keys(json);
keys.forEach(function(key) { json.renameKey(key, key.replace('element_', ''); });