How to split date strings in JavaScript array

Question

For the following Month/Day/Year datestring array...

const array1 = ["05/31/2022", "06/01/2022", "06/02/2022"]

...I am attempting to configure the array to slice and remove all datestring array items (starting with 01 as Day) if they follow after datestring array items with 31 as Day. Same goes for instances of Day 30 followed by Day 01.

To handle this, I set up a for statement to loop through all of the strings in the array. I then used a split method to remove "/" from each array item, thus breaking MM,DD,YYYY into separate variables.

for (let i = 0; i < array1.length; i++) {
  var [month, day, year] = array1[i].split('/');
  console.log(month, day, year)
}

My intention for the next step is to set up a conditional that checks if an array item that includes 30 or 31 as "day" is followed by an array item that includes 01 as "day", then use slice to remove subsequent dates faster 30th or 31st. For this part, I attempted to re-consolidate month, day and year into individual array items, like so:

const newArray = []

for (let i = 0; i < array1.length; i++) {
  var [month, day, year] = array1[i].split('/');
  newArray.push(month + day + year)
  console.log(newArray)
}

with output:

 ['05312022', '06012022', '06022022']

However, I'm not sure how to set up a conditional that checks if an array item that includes 30 or 31 as "day" is followed by an array item that includes 01 as "day". How can I go about the functionality for such a check?

Final array should be ["5/31/2022"]. If array item "05/31/2022" is followed by "06/01/2022", then all array items after "05/31/2022" should be removed. — JS_is_awesome18
– JS_is_awesome18, Commented May 15, 2022 at 16:43
Meaning in any instance where an array item with a day value of 31 is followed by an array item with a day value of 01, then all array items that come after the array item with day value 31 should be removed. — JS_is_awesome18
– JS_is_awesome18, Commented May 15, 2022 at 16:47
What should be the output for this array ["05/31/2022", "06/01/2022", "07/01/2022"]? — Som Shekhar Mukherjee
– Som Shekhar Mukherjee, Commented May 15, 2022 at 16:47

Som Shekhar Mukherjee · Accepted Answer · 2022-05-15 16:54:17Z

1

You can loop over the dates array and grab the currDay and prevDay and if the condition is satisfied, slice the dates array and return it.

const solution = (dates) => {
  for (let i = 1; i < dates.length; i++) {
    const currDay = dates[i].slice(3, 5);
    const prevDay = dates[i - 1].slice(3, 5);
    if ((currDay === "01") & (prevDay === "31" || prevDay === "30")) {
      return dates.slice(0, i);
    }
  }
  return dates;
};

console.log(solution(["05/31/2022", "06/01/2022", "06/02/2022"]));

answered May 15, 2022 at 16:54

Som Shekhar Mukherjee

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Comments

PeterKA · Accepted Answer · 2022-05-15 17:11:32Z

The following us es Array#reduce to

retain all elements unless
the number of elements retained equals the index being considered and the current element has date 01 and follows a 30 or a 31
if index in consideration is greater than the number of items retained, meaning at least one element has been skipped, then the current element is skipped as well.

const array1 = ["05/31/2022", "06/01/2022", "06/02/2022"],

      output = array1.reduce(
          (prev,cur,i) => 
          prev.length && ["30","31"].includes( prev.slice(-1)[0].slice(3,5) ) && 
          (prev.length === i && cur.slice(3,5) === "01" || i > prev.length) ?
              prev :
              [...prev, cur],
          []
      );
      
console.log( output );

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