How To Rewrite An Array.every() In A Custom Array.reduce() In Javascript?

This question is for purely for learning purposes. funfunfunction on youtube says that Any list higher order list transformation can be written in Array.reduce() Audio/video Re

Solution 1:

You can use reduce instead of every and make it work, but I'd suggest you to use them in there apt places. Both have distinctive requirement.

array.reduce

array.reduce(callback(curentElement, nextElement, index, array),[initialCurrentElement])

Array.reduce has 4 args.

• currentElement: By default, this will be 1st element in array for 1st iteration and then, this variable will hold value that you return. If an initial value is passed, then it will hold that and start from there.
• nextElement: By default it holds second or next element. If initial value is passed, this will hold first value.
• index: this holds the index of current element.
• array: This is the parent array on which we are looping.
• initialCurrentElement: This is an optional argument. If this is passed, looping starts with this.

Following is a sample showing an illustration:

Note:

• Array.every will break on first falsey condition. Array.reduce will not.
• Array.reduce is meant to compare 2 values of same array where as Array.every is meant to compare each values to an expression. Using .reduce instead of .every is just an overkill.

var approved2 = [{
  dateApproved: null,
  id: 1,
}, {
  dateApproved: newDate(),
  id: 2,
}];

var everyResult = approved2.every(x => {
  console.log(x.dateApproved)
  x.dateApproved !== null
})

console.log(everyResult)

var reduceResult = approved2.reduce((p, c) => {
  console.log(c.dateApproved)
  return !p ? p : c.dateApproved !== null
}, true)

console.log(reduceResult? 'Approved': 'Rejected')

Solution 2:

This should do the trick:

functionevery(pre, curr) {
  return pre.dateApproved != null && curr.dateApproved != null
}

approved1.reduce(every) ? 'APPROVED' : 'PENDING'// APPROVED
approved2.reduce(every) ? 'APPROVED' : 'PENDING'// PENDING

And I'm pretty sure you can do it without curr, just pre.

Solution 3:

var status = approved1.reduce(  val  =>  (val.dateApproved) ? 'APPROVED': 'REJECTED')

var approved1 = [

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

var approved2 = [

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

console.log(approved2.reduce(  (prev, curr)  =>  (prev.dateApproved && curr.dateApproved) ? true : false) ? 'APPROVED':'REJECTED')

console.log(approved1.reduce(  (prev, curr)  =>  (prev.dateApproved && curr.dateApproved) ? true : false) ? 'APPROVED':'REJECTED')

Solution 4:

You might roughly implement it as folows

Array.prototype.every = function(cb){
  returnthis.reduce((p,c,i,a) => i === 1 ? cb(p,i-1,a) && cb(c,i,a)
                                          : p && cb(c,i,a));
};

var arr = [9,2,3,9,12,5],
    brr = [1,2,3,4,5,6,9];
console.log(arr.every(e => e < 10));
console.log(brr.every(e => e < 10));