From array of Object , get array of only matched key value

Question

Suppose I have an array of object:

var students = [{name: 'Nick',achievements: 158,points: 1473}, {name: 'Nick',achievements: '175',points: '16375'}, 
{name: 'Ramon',achievements: '55',points: '2025'}];

I want to extract points from name Nick only in an array.

Like if (name=='Nick), O/P should be [1473,16375]

I tried:

var arrayPoints = students.map(function (el) { 
    if(el.name=='Nick'){
        return el.points
    }
});

But it gives me o/p:

console.log(arrayPoints)

[1473,16375,undefined] o/p

Answer 1

A look to the methods:

• Array#map returns a (new) value for each element.

• Array#filter returns exactly the element if the return value of the callback is truthy

---

You could take two steps, one for filtering the items and another to get the values from.

const
    students = [{ name: 'Nick', achievements: 158, points: 1473 }, { name: 'Nick', achievements: '175', points: '16375' }, { name: 'Ramon', achievements: '55', points: '2025' }],
    arrayPoints = students
        .filter(student => student.name === 'Nick') 
        .map(student => student.points);

console.log(arrayPoints);

If Array#flatMap is implemented, you could take a single loop and filter and return a value.

The empty array has no items and this array is a neutral value which does not turn up in the result array.

const
    students = [{ name: 'Nick', achievements: 158, points: 1473 }, { name: 'Nick', achievements: '175', points: '16375' }, { name: 'Ramon', achievements: '55', points: '2025' }],
    arrayPoints = students
        .flatMap(student => student.name === 'Nick'
            ? student.points
            : []
        );

console.log(arrayPoints);

Answer 2

For single loop result without undefined. You could do with Array#reduce

students.reduce(function (acc,el) { 
    if(el.name=='Nick'){
        acc.push(el.points)
    }
    return acc
},[]);