lodash pick: set value if key not set

Question

I have the following two arrays:

var headerKeys = ["title","name","address"]
var resultsArr = [
    { title:"test 1", name: "test1", unrelatedKey: "blah" },
    { title:"test 2", name: "test2" }
]

I'd like to clean up resultsArr such that it only has the keys found in headerKeys. My desired output looks like this:

[
    { title:"test 1", name: "test1", address: "" },
    { title:"test 2", name: "test2", address: "" }
]

This is the code I'm currently using:

_.chain(resultsArr).map(function(item){
    return _.chain(item).pick(headerKeys).value()
}).value()

This outputs:

[
    { title:"test 1", name: "test1" },
    { title:"test 2", name: "test2" }
]

It's pretty close to what I want, but it will not show address since it isn't set. Is there anyway to force it to show the key even if it has no value?

Also, if you have suggestions on how to improve my lodash chain, that would be great.

Answer 1

You can use _.defaults() to add the missing keys:

var headerKeys = ["title","name","address"]
var resultsArr = [
    { title:"test 1", name: "test1", unrelatedKey: "blah" },
    { title:"test 2", name: "test2" }
];

/** create once the defaults object from the headerKeys **/
var defaultsObj = _(headerKeys)
  .mapKeys()
  .mapValues(function() { return ""; })
  .value();

var result = resultsArr.map(function(obj) {
  return _(obj)
    .pick(headerKeys)
    .defaults(defaultsObj) // apply the defaults
    .value();
});

console.log(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.min.js"></script>

Answer 2

You can create a function getModel() to return your model, and then without lodash:

getModel= ()=>({ title:'', name:'', address:'default' });

var resultsArr = [
    { title:"test 1", name: "test1", unrelatedKey: "blah" },
    { title:"test 2", name: "test2" }
];

var result = resultsArr.map(function(obj) {
  var model = getModel();
  for (var key in model) {
    if (obj.hasOwnProperty(key)) {
      model[key] = obj[key];
    }
  }
  return model;
});

console.log(result)