Generate array of times (as strings) for every X minutes in JavaScript

Allocating the resulting array to avoid the overhead of push, parameter validation and locale specifics notwithstanding:

    function generate_series(step) {
        const dt = new Date(1970, 0, 1);
        const rc = [];
        while (dt.getDate() === 1) {
            rc.push(dt.toLocaleTimeString('en-US'));
            dt.setMinutes(dt.getMinutes() + step);
        }
        return rc;
    }

Here's a demo snippet.

function generate_series(step) {
  const dt = new Date(1970, 0, 1);
  const rc = [];
  while (dt.getDate() === 1) {
    rc.push(dt.toLocaleTimeString('en-US'));
    dt.setMinutes(dt.getMinutes() + step);
  }
  return rc;
}

function on_generate_series(step) {
  const dt = new Date(1970, 0, 1);
  const el = document.getElementById("series")
  while (el.firstChild)
    el.removeChild(el.firstChild);
  const series = generate_series(step);
  while (series.length > 0) {
    let item = document.createElement("div");
    item.innerText = series.shift();
    el.appendChild(item);
  }
}

<h1 id="title">24 Hour Minute Series</h1>
<input type="number" id="step" value="30" />
<input type="submit" id="byBtn" value="Generate Series" onclick="on_generate_series(parseInt(document.getElementById('step').value,10))" />
<div id="series">
</div>

The following is massively flexible with the help of Moment.js.

This code uses

• moment.duration
• moment.add

There's no error handling, so you can pass in stupid parameters, but it gets the point across. :-D

The desiredStartTime parameter takes a time in hh:mm format.

The period parameter accepts any of the moment.duration inputs.

const timelineLabels = (desiredStartTime, interval, period) => {
  const periodsInADay = moment.duration(1, 'day').as(period);

  const timeLabels = [];
  const startTimeMoment = moment(desiredStartTime, 'hh:mm');
  for (let i = 0; i <= periodsInADay; i += interval) {
    startTimeMoment.add(i === 0 ? 0 : interval, period);
    timeLabels.push(startTimeMoment.format('hh:mm A'));
  }

  return timeLabels;
};

/* A few examples */
const theDiv = document.getElementById("times");
let content;

content = JSON.stringify(timelineLabels('18:00', 2, 'hours'))
theDiv.appendChild(document.createTextNode(content));
theDiv.appendChild(document.createElement("p"));

content = JSON.stringify(timelineLabels('06:00', 30, 'm'))
theDiv.appendChild(document.createTextNode(content));
theDiv.appendChild(document.createElement("p"));

content = JSON.stringify(timelineLabels('00:00', 5, 'minutes'))
theDiv.appendChild(document.createTextNode(content));
theDiv.appendChild(document.createElement("p"));

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.18.1/moment.js"></script>

<div id="times"></div>

if you have access to moment, you can always do something like this:

const locale = 'en'; // or whatever you want...
const hours = [];

moment.locale(locale);  // optional - can remove if you are only dealing with one locale

for(let hour = 0; hour < 24; hour++) {
    hours.push(moment({ hour }).format('h:mm A'));
    hours.push(
        moment({
            hour,
            minute: 30
        }).format('h:mm A')
    );
}

the result is the following array:

["12:00 AM", "12:30 AM", "1:00 AM", "1:30 AM", "2:00 AM", "2:30 AM", "3:00 AM", "3:30 AM", "4:00 AM", "4:30 AM", "5:00 AM", "5:30 AM", "6:00 AM", "6:30 AM", "7:00 AM", "7:30 AM", "8:00 AM", "8:30 AM", "9:00 AM", "9:30 AM", "10:00 AM", "10:30 AM", "11:00 AM", "11:30 AM", "12:00 PM", "12:30 PM", "1:00 PM", "1:30 PM", "2:00 PM", "2:30 PM", "3:00 PM", "3:30 PM", "4:00 PM", "4:30 PM", "5:00 PM", "5:30 PM", "6:00 PM", "6:30 PM", "7:00 PM", "7:30 PM", "8:00 PM", "8:30 PM", "9:00 PM", "9:30 PM", "10:00 PM", "10:30 PM", "11:00 PM", "11:30 PM"]

This snippet generates a range base on locale, so you do not need to handle AM/PM manually. By default, it will use browser language, but you can pass a user-selected one.

function getTimeRanges(interval, language = window.navigator.language) {
    const ranges = [];
    const date = new Date();
    const format = {
        hour: 'numeric',
        minute: 'numeric',
    };

    for (let minutes = 0; minutes < 24 * 60; minutes = minutes + interval) {
        date.setHours(0);
        date.setMinutes(minutes);
        ranges.push(date.toLocaleTimeString(language, format));
    }

    return ranges;
}

console.log('English', getTimeRanges(30, 'en'));
console.log('Russian', getTimeRanges(30, 'ru'));

You need only one loop, follow this approach

var d = new Date(); //get a date object
d.setHours(0,0,0,0); //reassign it to today's midnight

Now keep adding 5 minutes till the d.getDate() value changes

var date = d.getDate();
var timeArr = [];
while ( date == d.getDate() )
{
   var hours = d.getHours();
   var minutes = d.getMinutes();
   hours = hours == 0 ? 12: hours; //if it is 0, then make it 12
   var ampm = "am";
   ampm = hours > 12 ? "pm": "am";
   hours = hours > 12 ? hours - 12: hours; //if more than 12, reduce 12 and set am/pm flag
   hours = ( "0" + hours ).slice(-2); //pad with 0
   minute = ( "0" + d.getMinutes() ).slice(-2); //pad with 0
   timeArr.push( hours + ":" + minute + " " + ampm );
   d.setMinutes( d.getMinutes() + 5); //increment by 5 minutes
}

Demo

Loops are unnecessary in this case.

ES6

//Array.from, only supported by Chrome 45+, Firefox 32+, Edge and Safari 9.0+
//create an array of the expected interval
let arr = Array.from({
  length: 24 * 60 / 5
}, (v, i) => {
  let h = Math.floor(i * 5 / 60);
  let m = i * 5 - h * 60;
  //convert to 12 hours time
  //pad zero to minute
  if (m < 10) {
    m = '0' + m;
  }
  let label = 'AM';
  if (h > 12) {
    label = 'PM';
    h -= 12;
  }
  if (h === 0) {
    h = 12;
  }
  return h + ':' + m + ' ' + label;
});

document.body.textContent = JSON.stringify(arr);

Wider browser support

var arr = Array.apply(null, {
  length: 24 * 60 / 5
}).map(function(v, i) {
  var h = Math.floor(i * 5 / 60);
  var m = i * 5 - h * 60;
  if (m < 10) {
    m = '0' + m;
  }
  var label = 'AM';
  if (h > 12) {
    label = 'PM';
    h -= 12;
  }
  if (h === 0) {
    h = 12;
  }
  return h + ':' + m + ' ' + label;
});

document.body.textContent = JSON.stringify(arr);

In any case you need to do O(N) operations to enumerate array elements. However, you could iterate through Date objects itself.

function timeArr(interval) //required function with custom MINUTES interval
{
  var result = [];
  var start = new Date(1,1,1,0,0);
  var end = new Date(1,1,2,0,0);
  for (var d = start; d < end; d.setMinutes(d.getMinutes() + 5)) {
      result.push(format(d));
  }

  return result;
}

function format(inputDate) // auxiliary function to format Date object
{
    var hours = inputDate.getHours();
    var minutes = inputDate.getMinutes();
    var ampm = hours < 12? "AM" : (hours=hours%12,"PM");
    hours = hours == 0? 12 : hours < 10? ("0" + hours) : hours;
    minutes = minutes < 10 ? ("0" + minutes) : minutes;
    return hours + ":" + minutes + " " + ampm;
}

Demo

You could use a single for loop, while loop , Array.prototype.map(), Array.prototype.concat() , String.prototype.replace()

var n = 0,
  min = 5,
  periods = [" AM", " PM"],
  times = [],
  hours = [12, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11];

for (var i = 0; i < hours.length; i++) {
  times.push(hours[i] + ":" + n + n + periods[0]);
  while (n < 60 - min) {
    times.push(hours[i] + ":" + ((n += 5) < 10 ? "O" + n : n) + periods[0])
  }
  n = 0;
}

times = times.concat(times.slice(0).map(function(time) {
  return time.replace(periods[0], periods[1])
}));

console.log(times)

My solution with emphasize on readability. It first creates objects that represent correct times and then formats them to strings. JsFiddle https://jsfiddle.net/6qk60hxs/

var periods = ['AM', 'PM'];
var hours = [12, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11];
var minutes = ["00", "05", 10, 15, 20, 25, 30, 35, 40, 45, 50, 55];


timeObj = add([{}], "p", periods);
timeObj = add(timeObj, "h", hours);
timeObj = add(timeObj, "m", minutes);

times = []
for (t of timeObj) {
  times.push(t.h + ':' + t.m + ' ' + t.p);
}

console.log(times)

function add(tab, prop, val) {
  var result = [];
  for (t of tab) {
    for (v of val) {
      tc = _.clone(t);
      tc[prop] = v;
      result.push(tc);
    }
  }
  return result
}

This is an iteration of Faizan Saiyed's answer.

const startHour = moment().format('k');
const endHour = 22

const arr = () => {
  return Array.from({
  length: endHour - startHour
  }, (v, index) => {
    return [0,15,30,45].map((interval) => {
      return moment({
        hour: index,
        minute: interval
      })
      .add(startHour, 'hours')
      .format('h:mm A')
    })
  }).flat()
}

Manipulating with a date as with integer and using single loop:

var interval = 5 * 60 * 1000; //5 minutes 
var period = 24 * 60 * 60 * 1000; //dat period

//just converts any time to desired string
var toString = function toString(time){  
  var h = time.getHours();
  var m = time.getMinutes();
  var p = h >= 12 ? "PM" : "AM";
  h = h || 12;
  h = h > 12 ? h - 12 : h;  
  return ("0" + h).slice(-2) + ":" + ("0" + m).slice(-2) + " " + p;
}

//start time
var time = new Date(2010, 0, 1);

//resulting array
var times = [];

for ( var t = +time; t < +time + period; t += interval){  
  var d = toString(new Date(t));  
  times.push(d);
}

const getTimes = (increment = 2) => {
  const times = [];
  for (let i = 0; i < 24; i++) {
    times.push({
      value: `${i === 0 || i - 12 === 0 ? 12 : i < 12 ? i : i - 12}:00 ${i < 12 ? 'AM' : 'PM'}`,
      label: `${i === 0 || i - 12 === 0 ? 12 : i < 12 ? i : i - 12}:00 ${i < 12 ? 'AM' : 'PM'}`,
    });
    for (let j = 60 / increment; j < 60; j += 60 / increment) {
      times.push({
        value: `${i === 0 || i - 12 === 0 ? 12 : i < 12 ? i : i - 12}:${Math.ceil(j)} ${i < 12 ? 'AM' : 'PM'}`,
        label: `${i === 0 || i - 12 === 0 ? 12 : i < 12 ? i : i - 12}:${Math.ceil(j)} ${i < 12 ? 'AM' : 'PM'}`,
      });
    }
  }
  return times;
};

The result of this is an array times converted into markup that I place in a <select> object. I found that underscore.js's _.range allows me to step through increments but only as integers. So, I used moment.js to convert to unix time. I needed to iterate over minutes slottime, but other intervals can be accomplished with the multiplier, again in my case 60000 making minutes added to valueOf().

function slotSelect(blockstart, blockend, slottime) {
    var markup = "";
    var secs = parseInt(slottime * 60000); // steps
    var a = parseInt( moment(blockstart).valueOf() ); // start
    var b = parseInt( moment(blockend).valueOf() );
    var times = _.range(a, b, secs);

    _.find( times, function( item ) {
        var appttime = moment(item).format('h:mm a');
        var apptunix = moment(item).format();
        markup += '<option value="'+apptunix+'"> ' + appttime + ' </option>'+"\n";
    });
    return markup;
}

To start list from particular time like 3:00 PM and loop quarterly(every 15 minutes):

const hours = [];
const startHour = 15;

for (let hour = 0; hour < 24; hour++) {
  hours.push(
    moment({ hour })
      .add(startHour, 'hours')
      .format('h:mm A')
  );

  hours.push(
    moment({
      hour,
      minute: 15
    })
      .add(startHour, 'hours')
      .format('h:mm A')
  );

  hours.push(
    moment({
      hour,
      minute: 30
    })
      .add(startHour, 'hours')
      .format('h:mm A')
  );

  hours.push(
    moment({
      hour,
      minute: 45
    })
      .add(startHour, 'hours')
      .format('h:mm A')
  );
}