Sort javascript object based on date keys

Question

I have a JavaScript object that looks like follows

testObj = {
    1/10/2015: {},
    2/10/2015: {},
    3/10/2015: {},
    4/10/2015: {},
    29/09/2015: {},
    30/09/2015: {}
}

Now, I'm trying to sort this such that the dates are arranged by date in increasing order. For that i've done the following

const orderedDates = {};
Object.keys(testObj).sort(function(a, b) {
    return moment(moment(b, 'DD/MM/YYYY') - moment(a, 'DD/MM/YYYY')).format('DD/MM/YYYY');
}).forEach(function(key) {
    orderedDates[key] = testObj[key];
})
rangeObj = orderedDates;

This however is not sorting the dates at all. It still returns the same exact object as testObj. How do I sort the object based on date keys?

Answer 1

This line returns a string:

moment(moment(b, 'DD/MM/YYYY') - moment(a, 'DD/MM/YYYY')).format('DD/MM/YYYY')

But the sort method requires an integer value, so you need to compare the actual dates instead:

Object.keys(testObj).sort(function(a, b) {
    return moment(b, 'DD/MM/YYYY').toDate() - moment(a, 'DD/MM/YYYY').toDate();
}).forEach(function(key) {
    orderedDates[key] = testObj[key];
})

However you need to be aware that in ES5, the order of keys in an object was not guaranteed by the spec - although most browsers did iterate the keys in insertion order. In ES6 however, you can be guaranteed that if you iterate your objects keys they will be in order.

So console.log(orderedDates) may not show the keys in your expected order, but Object.keys(orderedDates).forEach(function(date) { console.log(date); }); will work as expected.

var testObj = {
    "1/10/2015": {},
    "2/10/2015": {},
    "3/10/2015": {},
    "4/10/2015": {},
    "29/09/2015": {},
    "30/09/2015": {}
};
var orderedDates = {};
Object.keys(testObj).sort(function(a, b) {
    return moment(b, 'DD/MM/YYYY').toDate() - moment(a, 'DD/MM/YYYY').toDate();
}).forEach(function(key) {
    orderedDates[key] = testObj[key];
})
Object.keys(orderedDates).forEach(function(date) {
   document.body.innerHTML += date + "<br />"
});

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