Map, filter and reduce for functional programming

functional-1.js

var people = [
    {'name': 'Mary', 'height': 160},
    {'name': 'Isla', 'height': 80},
    {'name': 'Sam'}
];

var peopleWithHeight = people.filter(function(person) {
    return person.hasOwnProperty('height');
});

var heightTotal = peopleWithHeight
    .map(function(person){
        return person.height;
    })
    .reduce(function(accumulator, current){
       return accumulator + current;
    }, 0);


console.log(heightTotal/peopleWithHeight.length);