How to format a String to Date in React Native?

Amine Published at Dev

Amine

I am getting a Date as a String in this format from the server yyyyMMdd:hhmmss.

Is there a generic way to format this string to a Date object?

EDIT

 formatDate = (data) => {
    return data.slice(6, 8) + "." + data.slice(4, 6) + "." + data.slice(0, 4) + " " + data.slice(9, 11) + ":" + data.slice(11, 13)
}

RobG

The way you're reformatting the string is fine, even though it seems like a lot of code for a small job, slice is pretty fast. Some alternatives (not necessarily "better", just different):

// Reformat yyyyMMdd:hhmmss as dd.mm.yyyy hh:mm:ss
function formatMatch(s) {
  let b = s.match(/\d\d/g) || [];
  return `${b[3]}.${b[2]}.${b[0]}${b[1]} ${b[4]}:${b[5]}:${b[6]}`;
}

function formatReplace(s) {
  return s.replace(/(\d{4})(\d{2})(\d{2}):(\d{2})(\d{2})(\d{2})/, '$3.$2.$1 $4:$5:$6');
}

formatDate = (data) => {
    return data.slice(6, 8) + "." + data.slice(4, 6) + "." + data.slice(0, 4) + " " + data.slice(9, 11) + ":" + data.slice(11, 13)
}

let s = '20200323:123445';
console.log(formatDate(s));
console.log(formatMatch(s));
console.log(formatReplace(s));

If you want to get an actual Date object, then instead of using the bits to create another string, just pass them into the constructor:

// Parse yyyyMMdd:hhmmss to Date object
function parseD(s) {
  let b = s.match(/\d\d/g) || [];
  return new Date(b[0]+b[1], b[2]-1, b[3], b[4], b[5], b[6]);
}

let s = '20200327:134523';
console.log(parseD(s).toString());

The use of || [] means that if there's no match, an empty array is returned so all the b[*] terms return undefined and the result is an invalid date.

The above uses match, but slice or substring can be used the same way.

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