[Solved] JavaScript : How to calculate days count from two dates based on month

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In the spirit of teaching, see comments:

var stopDate = new Date("2014-09-04");  // One day AFTER the last date we care
                                        // about
var results = [];                       // An array for our results, initially
                                        // empty
var date = new Date("2014-08-28");      // Our starting date
var entry;                              // The "current" month's entry in the loop
while (date < stopDate) {

    // Create a new entry if necessary.
    // The `!entry` bit uses the fact that variables start out with the value
    // `undefined`, and `undefined` is "falsey", so `!entry` will be true if
    // we haven't put anything in `entry` yet. If we have, it's an object
    // reference, and object references are "truthy", so `!entry` will be
    // false. The second check is to see whether we've moved to a new month.
    if (!entry || entry.month !== date.getMonth() + 1) {

        // Create a new entry. This creates an object using an object initialiser
        // (sometimes called an object "literal")
        entry = {
            month: date.getMonth() + 1, // +1 because `getMonth` uses 0 = January
            days:  0                    // Haven't counted any days yet
        };

        // Add it to the array
        results.push(entry);
    }

    // Count this day
    ++entry.days;

    // Move to next day
    date.setDate(date.getDate() + 1);   // JavaScript's `Date` object handles
                                        // moving to the next month for you
}

About “falsey” and “truthy”: In most languages, you can only use booleans (true or false) for branching, but JavaScript allows coercing values to booleans. “Falsey” values are values that coerce to false. They are: undefined, null, NaN, 0, "", and of course false. “Truthy” values are everything else.

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solved JavaScript : How to calculate days count from two dates based on month