basic-date-math.js

const MATCH = /^(-|\+)([1-9][0-9]{0,2})(h|d|w|m|y)(\/d)?$/

const isDateMathExpression = (dateStr) => {
    return typeof dateStr === 'string' && MATCH.test(dateStr)
}

const parseDateMathExpression = (dateStr) => {
    const [match, operator, number, unit, round] = MATCH.exec(dateStr) || []

    if (match) {
        const factor = operator === '-' ? -1 : 1
        const value = parseInt(number, 10) * factor

        let date = new Date()

        if (round) {
            date = new Date(date.toISOString().slice(0, 10))
        }

        switch (unit) {
            case 'h':
                date.setHours(date.getHours() + value)
                break
            case 'd':
                date.setDate(date.getDate() + value)
                break
            case 'w':
                date.setDate(date.getDate() + (value * 7))
                break
            case 'm':
                date.setMonth(date.getMonth() + value)
                break
            case 'y':
                date.setFullYear(date.getFullYear() + value)
                break
        }

        return date
    }
}


console.log('Addition:')
console.log(parseDateMathExpression('+1h'))
console.log(parseDateMathExpression('+1d/d'))
console.log(parseDateMathExpression('+1w/d'))
console.log(parseDateMathExpression('+1m/d'))
console.log(parseDateMathExpression('+1y/d'))
console.log('Subtraction:')
console.log(parseDateMathExpression('-1h'))
console.log(parseDateMathExpression('-1d/d'))
console.log(parseDateMathExpression('-1w/d'))
console.log(parseDateMathExpression('-1m/d'))
console.log(parseDateMathExpression('-1y/d'))