Retrieve JSON values in Javascript

Question

I have to create a JSON from a first JSON.

{  
        "event":"comprou",
        "timestamp":"2016-09-22T13:57:31.2311892-03:00",
        "revenue":250,
        "custom_data":[  
            {  
                "key":"store_name",
                "value":"Patio Savassi"
            },
            {  
                "key":"transaction_id",
                "value":"3029384"
            }
        ]
    }

The one I have to create, the structure has to be that kind:

{
  "timestamp": "2016-10-02T11:37:31.2300892-03:00",
  "revenue": 120.0,
  "transaction_id": "3409340",
  "store_name": "Loja do Pedro"
}

How can I access the transaction_id and the store_name?

Answer 1

First Form:

You can create a custom function to format the data the way you want. In the example below, the function formatJSON creates an object with two initial properties (timestamp and revenue). After that, a loop is made about the array custom_data, adding the other values to the object.

const first = {  
  event: 'comprou',
  timestamp: '2016-09-22T13:57:31.2311892-03:00',
  revenue: 250,
  custom_data: [  
    {  
        key: 'store_name',
        value: 'Patio Savassi'
    },
    {  
        key: 'transaction_id',
        value: '3029384'
    }
  ]
};

function formatJSON (data) {
  const object = {
    timestamp: data.timestamp,
    revenue: data.revenue
  };

  for (const customData of data.custom_data) {
    object[customData.key] = customData.value;
  }

  return object;
}

console.log(formatJSON(first));

Note that to shorten the code, we can rewrite the function formatJSON, using a new Javascript feature, called destructuring:

function formatJSON ({ timestamp, revenue, custom_data: data }) {
  const object = { timestamp, revenue };

  for (const { key, value } of data) {
    object[key] = value;
  }

  return object;
}

Second form:

If you simply want to access the properties store_name and transaction_id, can do so:

const oldObject = {  
  event: 'comprou',
  timestamp: '2016-09-22T13:57:31.2311892-03:00',
  revenue: 250,
  custom_data: [  
    {  
        key: 'store_name',
        value: 'Patio Savassi'
    },
    {  
        key: 'transaction_id',
        value: '3029384'
    }
  ]
};

const newObject = {
  timestamp: oldObject.timestamp,
  revenue: oldObject.revenue,
  store_name: oldObject.custom_data[0].value,
  transaction_id: oldObject.custom_data[1].value
};

console.log(newObject);

Like custom_data is a array, we can access a specific element using its index, through the notation array[index]. To learn more, read that documentation about arrays on MDN.

Addendum:

Remember that to convert a string for JSON (object in Javascript), use:

JSON.parse('{ "hello": "world" }');

And to transform a JSON (object) into string, utilize:

JSON.stringify({ hello: 'world' });

Reference:

• JSON.parse();
• JSON.stringify().