Time difference in Javascript

Question

I have a textbox where I get the time as HH:MM AM/PM (like 5:30 PM). I want to validate the time: whether it is 1 hour greater than the current time or not. How can I do this using JavaScript?

Answer 1

First of all, I'd suggest using an existing date-handling library like Datejs. You will have the benefit if a time-tested library with a comprehensive set of methods.

With Datejs, your answer is as simple as:

Date.parse(timeText).isAfter((new Date()).addHours(1));

If you'd rather not use Datejs, you can use regular expressions to parse the time before validating it. I've written a set of functions, along with unit tests which run in the Firebug console, that do just that:

function isOneHourGreater(timeText, time) {
  var parsedTime = parseTime(timeText);
  if (parsedTime === null) { return null; }
  return (parsedTime.getTime() - time.getTime()) > (1 * 60 * 60 * 1000);
}

function parseTime(timeText) {
  timeText = timeText.replace(/^\s+|\s$/g, '');
  var regex = /^(\d{1,2}):(\d{1,2})\s*(am|pm)$/i;

  if (!regex.test(timeText)) { return null; }

  var
    timeParts = regex.exec(timeText)
    , hours = parseInt(timeParts[1])
    , ampm = timeParts[3].toLowerCase()
    , hoursOffset = (ampm === 'pm' && hours !== 12) ? 12 : 0;

  hoursOffset = (ampm === 'am' && hours === 12) ? -12 : hoursOffset;

  return getTodayWithTime(
    hours + hoursOffset
    , parseInt(timeParts[2])
  );
}

function getTodayWithTime(hours, minutes) {
  var today = new Date();
  today.setHours(hours);
  today.setMinutes(minutes);
  today.setSeconds(0);
  today.setMilliseconds(0);
  return today;
}

function parseTimeTests() {
  var now = new Date();

  var tests = [
    {target: "12:00 am", expected: getTodayWithTime(0, 00)}
    , {target: "12:01 am", expected: getTodayWithTime(0, 01)}
    , {target: "12:00 pm", expected: getTodayWithTime(12, 00)}
    , {target: "12:01 pm", expected: getTodayWithTime(12, 01)}
    , {target: "1:30 Pm", expected: getTodayWithTime(13, 30)}
    , {target: "10:59 Pm", expected: getTodayWithTime(22, 59)}
    , {target: "0:30 Pm", expected: getTodayWithTime(12, 30)}
    , {target: "1:40 aM", expected: getTodayWithTime(1, 40)}
    , {target: " 6:15  am ", expected: getTodayWithTime(6, 15)}
    , {target: " 6:15am ", expected: getTodayWithTime(6, 15)}

    , {target: "006:15am", expected: null}
    , {target: "06:015am ", expected: null}
    , {target: "06:15amm ", expected: null}
    , {target: "a6:15am ", expected: null}
    , {target: "6: 15am", expected: null}
    , {target: "6:15", expected: null}
  ];

  for (var ii = 0; ii < tests.length; ii++) {
    var test = tests[ii];

    var actual = parseTime(test.target);

    console.assert(
      (actual === null && actual === test.expected)
      || (actual && test.expected && actual.getTime() === test.expected.getTime())
      , ii + 1 + " Failed"
      , test.target, test.expected, actual
    );
  }

  console.log('done');
}
parseTimeTests()

function isOneHourGreaterTests() {
  var mockTime = getTodayWithTime(14, 00);

  var tests = [
    {target: "3:01 pm", expected: true}
    , {target: "3:30 pm", expected: true}
    , {target: "11:59 pm", expected: true}
    , {target: "10:30 pm", expected: true}

    , {target: "2:59 pm", expected: false}
    , {target: "2:01 pm", expected: false}
    , {target: "2:30 pm", expected: false}
    , {target: "2:00 pm", expected: false}
    , {target: "10:30 am", expected: false}
    , {target: "1:40 pm", expected: false}
    , {target: "1:15 pm", expected: false}
    , {target: "6:15 am", expected: false}

    , {target: "a6:15 am", expected: null}
  ];

  for (var ii = 0; ii < tests.length; ii++) {
    var test = tests[ii];

    var actual = isOneHourGreater(test.target, mockTime);

    console.assert(
      (actual === null && actual === test.expected)
      || (actual === test.expected)
      , ii + 1 + " Failed"
      , test.target, test.expected, actual
    );
  }

  mockTime = getTodayWithTime(23, 00);

  tests = [
    {target: "1:01 am", expected: false}
    , {target: "12:01 am", expected: false}
    , {target: "2:30 am", expected: false}

    , {target: "11:59 pm", expected: false}
    , {target: "11:00 pm", expected: false}
    , {target: "11:01 pm", expected: false}

    , {target: "2:30 pm", expected: false}
    , {target: "2:00 pm", expected: false}
    , {target: "10:30 am", expected: false}
    , {target: "1:40 pm", expected: false}
    , {target: "1:15 pm", expected: false}
    , {target: "6:15 am", expected: false}

    , {target: "a6:15 am", expected: null}
  ];

  for (var ii = 0; ii < tests.length; ii++) {
    var test = tests[ii];

    var actual = isOneHourGreater(test.target, mockTime);

    console.assert(
      (actual === null && actual === test.expected)
      || (actual === test.expected)
      , ii + 1 + " Failed"
      , test.target, test.expected, actual
    );
  }

  console.log('done');
}
isOneHourGreaterTests();