ES6 tagged template string for inline date fomatting

moment-tags.js

/**
 * This doesn't _need_ to use moment.
 * It's just the library that this project is using.
 * Luxon or date-fns could also drop in neatly.
 */
const moment = require('moment')

// This a bad name, as is 'format', so idk.
function inline(literals, ...parts) {
    let join = '';
    let locations = {};
    
    // collecting part locations
    //  'abc ${a}|fmt| abc ${b} abc'
    // becomes:
    //  'abc |||fmt| abc || abc||'
    for (let i in literals) {
        join += literals[i] + '||'; // this marks non-formatted values
        locations[join.length - 2] = parts[i];
    }
    
    console.log(join)
    
    // regex offsets will match locations, format appropriately
    // matching '||' or '|||fmt|'
    return join.replace(/\|\|(?:\|([^|]*)\|)?/g, (m, fmt, i) => (
        moment.isMoment(locations[i])
            ? locations[i].format(fmt)
            : (locations[i] || '')
    ));
}

// test
if (require.main === module) {
    let m = moment(new Date());
    let mm = moment(new Date(1111234567890));
    let mmm = 'I am not a moment';
    
    console.log(inline`
        the date is ${m}|DD MMM YYYY|
        another ${mm}|ddd|
        <p>lastly ${mmm}</p>
    `)
}