Are there any higher order function to return an object from an array of objects in javascript?

问题

LIVE CODE EXAMPLE:

Background:

Trying to learn javascript's higher order function, some redux theory and applying it through a data transformations example and have been failing for the last few hours. :(

Question:

How can I iterate over the approved1 or approved2 and return a new object bases on 2 cases. Furthermore, is there a way to do this with a higher order function like Array.reduce() or a combination baked in higher order functions? Lastly, if the final Object is wrapped in an array thats fine too.

I want this for a few reasons:

• immutability.
• ease of testing.
• learning purposes.

The 2 cases:

• If all dateApproved values are !== null (in this example: approval1 array) then return a new Object (or Array wrapped Object) which looks like:

  {type: 'APPROVED', approvals: [...approved1]}

• If any of the dateApproved values are equal to null (in this example: approval2 array) return a new Object (or Array wrapped Object) which looks like:

  {type: 'PENDING', approvals: [...approved2]}

---

JAVASCRIPT:

// With given logic this array evaluate with a type of 'APPROVED'
var approved1 = [

    {
        dateApproved: new Date(),
        id: 1,
    },
    {
        dateApproved: new Date(),
        id: 2,
    }
];

// With given logic this array evaluate with a type of 'PENDING'
var approved2 = [

    {
        dateApproved: null,
        id: 1,
    },
    {
        dateApproved: new Date(),
        id: 2,
    }
];

// This reducer does nothing proper right now just placeholder.
function isApproved(previousValue, currentValue, currentIdx) {
    var TYPE = ['APPROVED', 'PENDING'];
    if(previousValue.dateApproved !== null && currentValue.dateApproved !== null) {

      return currentValue
    }
}

var x = approved1.reduce(isApproved);
console.log(x); // LOG: {type: 'APPROVED' approvals: [...approved1]}

var y = approved2.reduce(isApproved);
console.log(x); // LOG: {type: 'PENDING' approvals: [...approved2]}

回答1:

Use Array.prototype.every:

function wrap(approvals) {
  return {
    type: approvals.every(a => a.dateApproved != null) ? 'APPROVED' : 'PENDING',
    approvals: approvals
  };
}

wrap(approved1);
// => Object {type: "APPROVED", approvals: Array[2]}

wrap(approved2);
// => Object {type: "PENDING", approvals: Array[2]}

来源：https://stackoverflow.com/questions/40145757/are-there-any-higher-order-function-to-return-an-object-from-an-array-of-objects