Check array of dates to see if increasing

Question

I want to check an array of dates to see if they are increasing. For example, ['12/12/2023','13/12/2023'] would return true. However, ['12/12/2023','11/12/2023'] would return false. I have been playing around with a function suggested by users for checking integer values. I thought I could do the same but use dates instead.

Here is the function:

function isIncreasing(dates) {
    for (var i = 1; i < dates.length; i++) {
        let convertedToDate = new Date(dates[i]);
        //console.log(currentDate);
        if (convertedToDate[i] !== convertedToDate[i - 1] && convertedToDate[i] != convertedToDate[i - 1] + 1) {
            return false;
        }
    }
    return true;
}
console.log(isIncreasing(['12/12/2023','11/12/2023','10/12/2023']))

The function does not work as the above returns true. Any help is appreciated.

Answer 1

I managed to resolve it by converting the date to a timestamp before comparing. This works if the date is in the format (Y-m-d). Here is the final:

function isIncreasing(dates) {
    let prevDate = new Date(dates[0]).getTime();
    for (var i = 1; i < dates.length; i++) {
        let convertedToDate = new Date(dates[i]).getTime();
        if (prevDate > convertedToDate) {
            return false;
        }
        prevDate = convertedToDate
    }
    return true;
}

console.log(isIncreasing(['2023/12/12','2023/12/13','2023/12/14','2021/12/12']))
console.log(isIncreasing(['2023/12/12','2023/12/13','2023/12/14']))

Answer 2

Just split the dates by / and compare the numbers:

const isIncreasing = dates => {
  for(let i=1;i<dates.length;i++){
    const prev = dates[i-1].split('/');
    const curr = dates[i].split('/');
    for(let j = prev.length - 1;j >=0;j--){
       if(+curr[j] < +prev[j]) return false;
    }
  }
  return true;
}

console.log(isIncreasing(['12/12/2023','13/12/2023']))
console.log(isIncreasing(['12/12/2023','11/12/2023']))
console.log(isIncreasing(['12/12/2023','13/12/2023', '11/12/2023']))