Compare Dates

Compare two dates

BeginnerTopic: Date/Time Programs

JavaScript Compare Dates Program

This program helps you to learn the fundamental structure and syntax of JavaScript programming.

// Method 1: Compare timestamps
function compareDates(date1, date2) {
    if (date1.getTime() === date2.getTime()) {
        return 0; // Equal
    } else if (date1.getTime() > date2.getTime()) {
        return 1; // date1 is later
    } else {
        return -1; // date1 is earlier
    }
}

const date1 = new Date('2024-01-15');
const date2 = new Date('2024-01-20');
console.log('Compare:', compareDates(date1, date2));

// Method 2: Simple comparisons
console.log('date1 > date2:', date1 > date2);
console.log('date1 < date2:', date1 < date2);
console.log('date1 === date2:', date1.getTime() === date2.getTime());

// Method 3: Check if date is in range
function isDateInRange(date, startDate, endDate) {
    return date >= startDate && date <= endDate;
}

const checkDate = new Date('2024-01-18');
const start = new Date('2024-01-15');
const end = new Date('2024-01-20');
console.log('In range:', isDateInRange(checkDate, start, end));

// Method 4: Check if date is today
function isToday(date) {
    const today = new Date();
    return date.getDate() === today.getDate() &&
           date.getMonth() === today.getMonth() &&
           date.getFullYear() === today.getFullYear();
}

console.log('Is today:', isToday(new Date()));

// Method 5: Check if date is past/future
function isPast(date) {
    return date < new Date();
}

function isFuture(date) {
    return date > new Date();
}

console.log('Is past:', isPast(new Date('2020-01-01')));
console.log('Is future:', isFuture(new Date('2025-01-01')));

// Method 6: Compare dates (ignore time)
function compareDatesOnly(date1, date2) {
    const d1 = new Date(date1.getFullYear(), date1.getMonth(), date1.getDate());
    const d2 = new Date(date2.getFullYear(), date2.getMonth(), date2.getDate());
    return d1.getTime() - d2.getTime();
}

const dateWithTime = new Date('2024-01-15T15:30:00');
const dateWithoutTime = new Date('2024-01-15T00:00:00');
console.log('Same date (ignore time):', compareDatesOnly(dateWithTime, dateWithoutTime) === 0);

Output

Compare: -1
date1 > date2: false
date1 < date2: true
date1 === date2: false
In range: true
Is today: true
Is past: true
Is future: true
Same date (ignore time): true

Understanding Compare Dates

Date comparison checks relationships.

Comparison Methods

•getTime(): Compare timestamps

•Direct comparison: >, <, ===

•Date methods: getDate, getMonth, etc.

Common Checks

•Equal: getTime() === getTime()

•Before: date1 < date2

•After: date1 > date2

•In range: start <= date <= end

Date-Only Comparison

•Ignore time component

•Compare year/month/day only

•Useful for date ranges

Best Practices

•Use getTime() for equality

•Handle timezone issues

•Compare dates only when needed

•Use helper functions

Let us now understand every line and the components of the above program.

Note: To write and run JavaScript programs, you need to set up the local environment on your computer. Refer to the complete article Setting up JavaScript Development Environment. If you do not want to set up the local environment on your computer, you can also use online IDE to write and run your JavaScript programs.

Practical Learning Notes for Compare Dates

This JavaScript program is part of the "Date/Time Programs" topic and is designed to help you build real problem-solving confidence, not just memorize syntax. Start by understanding the goal of the program in plain language, then trace the logic line by line with a custom input of your own. Once you can predict the output before running the code, your understanding becomes much stronger.

A reliable practice pattern is to run the original version first, then modify only one condition or variable at a time. Observe how that single change affects control flow and output. This deliberate style helps you understand loops, conditions, and data movement much faster than copying full solutions repeatedly.

For interview preparation, explain this solution in three layers: the high-level approach, the step-by-step execution, and the time-space tradeoff. If you can teach these three layers clearly, you are ready to solve close variations of this problem under time pressure.

Timezone Conversion

Date Arithmetic