Extract fields from Json based on a list in Javascript

Question

I'm trying to extract some of the fields from a Json response and push them into a Javascript array. I want the selection of the fields to be configurable. Here is what I'm doing:

Consider this as my JSON string:

{
    "id" : "1234",
    "orderNumber" : "1196",
    "createdOn" : "2019-07-02T12:03:39.697Z",
    "modifiedOn" : "2019-07-02T12:25:52.126Z",
    "testmode" : false,
    "customerEmail" : "a@b.com",
    "billingAddress" : {
      "firstName" : "John",
      "lastName" : "Doe",
      "address1" : "Wall Street",
      "address2" : null,
      "city" : "NYC",
      "state" : "NY",
      "countryCode" : "US",
      "postalCode" : "12345",
      "phone" : "1122334455"
    }
}

Say I want to extract some of the fields (defined in the FIELDS variable) and push them in an array.

# NOTE: the variable `data` here is my json object 

var FIELDS = ['id', 'orderNumber', 'customerEmail', 'billingAddress.firstName', 'billingAddress.lastName']

var lineItem = []

# parse the data (my Json object)
for (var i = 0; i < FIELDS.length; i++){
  lineItem.push(data[FIELDS[i]])
}

So, this seems to be working OK for the first level (the id, orderNumber and customerEmail) but not for the billingAddress.firstname, etc. This is what I'm wondering about.

My intent is to be able to modify the definition in the FIELDS variable without needing to make any change to the logic in the code.

Hope this makes sense. Thanks!

how are you creating the `FIELDS` array from the JSON object? — Mr-K10, Jul 09 '19 at 19:02
@Mr-K10 He isn't. That array is the list of fields he wants to extract from the object. — , Jul 09 '19 at 19:05

score 1 · Answer 1 · answered Jul 09 '19 at 19:05

As long as there are no periods in the key names this will work.

var data = {
    "id" : "1234",
    "orderNumber" : "1196",
    "createdOn" : "2019-07-02T12:03:39.697Z",
    "modifiedOn" : "2019-07-02T12:25:52.126Z",
    "testmode" : false,
    "customerEmail" : "a@b.com",
    "billingAddress" : {
      "firstName" : "John",
      "lastName" : "Doe",
      "address1" : "Wall Street",
      "address2" : null,
      "city" : "NYC",
      "state" : "NY",
      "countryCode" : "US",
      "postalCode" : "12345",
      "phone" : "1122334455"
    }
};

var FIELDS = ['id', 'orderNumber', 'customerEmail', 'billingAddress.firstName', 'billingAddress.lastName'];

var lineItem = [];
for (var i = 0; i < FIELDS.length; i++){
  let obj = data;
  let parts = FIELDS[i].split(".");
  while(parts.length) obj = obj[parts.shift()];
  lineItem.push(obj)
}

console.log(lineItem);

score 1 · Answer 2 · answered Jul 09 '19 at 19:06

You just need a function that will split that path on . and traverse the JSON data. With that you can just map() over your fields.

let data = {"id" : "1234","orderNumber" : "1196","createdOn" : "2019-07-02T12:03:39.697Z","modifiedOn" : "2019-07-02T12:25:52.126Z","testmode" : false,"customerEmail" : "a@b.com","billingAddress" : {"firstName" : "John","lastName" : "Doe","address1" : "Wall Street","address2" : null,"city" : "NYC","state" : "NY","countryCode" : "US","postalCode" : "12345","phone" : "1122334455"}}
var FIELDS = ['id', 'orderNumber', 'customerEmail', 'billingAddress.firstName', 'billingAddress.lastName']

// split an traverse
const getFromPath = (path, data) => path.split('.')
      .reduce((curr, p) => curr && curr[p], data) // check for curr incase path is undefined
      
console.log(FIELDS.map(p => getFromPath(p, data)))

The function getFromPath will return undefined if any part of the traversal is not found in the object.

I like your use of reduce here! :) – IceMetalPunk Jul 09 '19 at 20:04 — IceMetalPunk, Jul 09 '19 at 20:04

Extract fields from Json based on a list in Javascript

2 Answers2