Sorting an array of objects by key

sort-array-of-objects.js

var arr = [
    {first: 'Joseph', last: 'Smith'}, 
    {first: 'Joseph', last: 'Chapman'}, 
    {first: 'Joseph', last: 'Hinge'}
];
    
var sortBy = function (key) {
    return function (o, p) {
        var a, b;
        if (o && p && typeof o === 'object' && typeof p === 'object') {
            a = o[key];
            b = p[key];
            if (a === b) {
                return 0;
            }
            if (typeof a === typeof b) {
                return a < b ? -1 : 1;
            }
            return typeof a < typeof b ? -1 : 1;
        }
    }        
};

arr.sort(sortBy('last'));

// arr is [{first: 'Joseph', last: 'Chapman'}, {first: 'Joseph', last: 'Hinge'}, {first: 'Joseph', last: 'Smith'}]