Moment JS duration humanize more precise

I solved your problem with this snippet of code I made.

function formatDuration(period) {
    let parts = [];
    const duration = moment.duration(period);

    // return nothing when the duration is falsy or not correctly parsed (P0D)
    if(!duration || duration.toISOString() === "P0D") return;

    if(duration.years() >= 1) {
        const years = Math.floor(duration.years());
        parts.push(years+" "+(years > 1 ? "years" : "year"));
    }

    if(duration.months() >= 1) {
        const months = Math.floor(duration.months());
        parts.push(months+" "+(months > 1 ? "months" : "month"));
    }

    if(duration.days() >= 1) {
        const days = Math.floor(duration.days());
        parts.push(days+" "+(days > 1 ? "days" : "day"));
    }

    if(duration.hours() >= 1) {
        const hours = Math.floor(duration.hours());
        parts.push(hours+" "+(hours > 1 ? "hours" : "hour"));
    }

    if(duration.minutes() >= 1) {
        const minutes = Math.floor(duration.minutes());
        parts.push(minutes+" "+(minutes > 1 ? "minutes" : "minute"));
    }

    if(duration.seconds() >= 1) {
        const seconds = Math.floor(duration.seconds());
        parts.push(seconds+" "+(seconds > 1 ? "seconds" : "second"));
    }

    return "in "+parts.join(", ");
}

This function takes a period string (ISO 8601), parses it with Moment (>2.3.0) and then, for every unit of time, pushes a string in the parts array. Then everything inside the parts array gets joined together with ", " as separation string.

You can test it here: https://jsfiddle.net/mvcha2xp/6/

I'm using it as a Vue filter to humanize durations correctly.

No. The only argument that .humanize() takes is the suffix toggle. If you check the source for the internal function that the humanize method uses, you can see that it always rounds the durations. If you want more specificity, you'll need to implement your own method with the desired behavior.

You can customize the output of relative time functions like humanize() using relativeTime key of updateLocale and relativeTimeThreshold.

I don't know what is your expected output for a generic duration, but you can use the following code to get in 14 seconds for a duration of 14 seconds:

const startTime = moment();
const end = moment().add(14, 'seconds');
const duration = moment.duration(end.diff(startTime));
console.log( duration.humanize(true) );

moment.relativeTimeThreshold('ss', 60);
moment.updateLocale('en', {
  relativeTime : {
    s: function (number, withoutSuffix, key, isFuture){
      return number + ' seconds';
    }
  }
});

console.log( moment.duration(end.diff(startTime)).humanize(true) );

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.22.2/moment.min.js"></script>

You can also take a look at this and this similar questions.