How to rename JSON key

As mentioned by evanmcdonnal, the easiest solution is to process this as string instead of JSON,

var json = [{"_id":"5078c3a803ff4197dc81fbfb","email":"[email protected]","image":"some_image_url","name":"Name 1"},{"_id":"5078c3a803ff4197dc81fbfc","email":"[email protected]","image":"some_image_url","name":"Name 2"}];
    
json = JSON.parse(JSON.stringify(json).split('"_id":').join('"id":'));

document.write(JSON.stringify(json));

This will convert given JSON data to string and replace "_id" to "id" then converting it back to the required JSON format. But I used split and join instead of replace, because replace will replace only the first occurrence of the string.

1. Parse the JSON

const arr = JSON.parse(json);

2. For each object in the JSON, rename the key:

obj.id = obj._id;
delete obj._id;

3. Stringify the result

All together:

function renameKey ( obj, oldKey, newKey ) {
  obj[newKey] = obj[oldKey];
  delete obj[oldKey];
}

const json = `
  [
    {
      "_id":"5078c3a803ff4197dc81fbfb",
      "email":"[email protected]",
      "image":"some_image_url",
      "name":"Name 1"
    },
    {
      "_id":"5078c3a803ff4197dc81fbfc",
      "email":"[email protected]",
      "image":"some_image_url",
      "name":"Name 2"
    }
  ]
`;
   
const arr = JSON.parse(json);
arr.forEach( obj => renameKey( obj, '_id', 'id' ) );
const updatedJson = JSON.stringify( arr );

console.log( updatedJson );

JSON.parse has two parameters. The second parameter, reviver, is a transform function that can format the output format we want. See ECMA specification here.

In reviver function:

• if we return undefined, the original property will be deleted.
• this is the object containing the property being processed as this function, and the property name as a string, the property value as arguments of this function.

const json = '[{"_id":"5078c3a803ff4197dc81fbfb","email":"[email protected]","image":"some_image_url","name":"Name 1"},{"_id":"5078c3a803ff4197dc81fbfc","email":"[email protected]","image":"some_image_url","name":"Name 2"}]';

const obj = JSON.parse(json, function(k, v) {
    if (k === "_id") {
        this.id = v;
        return; // if return  undefined, orignal property will be removed
    }
    return v;
});

const res = JSON.stringify(obj);
console.log(res)

output:

[{"email":"[email protected]","image":"some_image_url","name":"Name 1","id":"5078c3a803ff4197dc81fbfb"},{"email":"[email protected]","image":"some_image_url","name":"Name 2","id":"5078c3a803ff4197dc81fbfc"}]

In this case it would be easiest to use string replace. Serializing the JSON won't work well because _id will become the property name of the object and changing a property name is no simple task (at least not in most langauges, it's not so bad in javascript). Instead just do;

jsonString = jsonString.replace("\"_id\":", "\"id\":");