Convert a non separated String to javascript date

Question

I have a string like 20221004093142Z which I need to convert into a datetime format in JavaScript. Can someone help me on this?

Answer 1

Maybe you can use a RegExp to convert your input string to an ISO date formatted string (which is the closest to your input string) and then create a date from that formatted string. Something like:

const inputStr = '20221004093142Z'
const re = /(\d{4})(\d{2})(\d{2})(\d{2})(\d{2})(\d{2})(\.\d{0,3})?/g;
const formattedStr = inputStr.replace(re, '$1-$2-$3T$4:$5:$6$7');
const outputDate = new Date(formattedStr);

console.log(`inputStr: ${inputStr}`);
console.log(`formattedStr: ${formattedStr}`);
console.log(`outputDate: ${outputDate}`);
console.log(`outputDate.toLocaleString(): ${outputDate.toLocaleString()}`);

The Regular Expression (RegExp) explained:

• parentheses (()) delimit what is called a "capturing group", which can then be referred to by its position (e.g. $1 is the content of the first capturing group, $2 of the second, etc.)
• \d matches any digit (0-9)
• the curly brackets ({}) mark a quantifier: how many occurrences of the preceding character or group should I look for? You can provide an exact quantity ({4} -> exact 4) or a range ({0,3} -> from 0 up to 3)
• the question mark (?) indicates that the preceding character or group is optional (there can be zero or exactly one occurrence, but no more than one)

So what the RegExp proposed does is to look for

1. a group of four digits ((\d{4})), which will be referenced as $1, followed by
2. a group of two digits ((\d{2})), which will be referenced as $2, followed by
3. a group of two digits ((\d{2})), which will be referenced as $3, followed by
4. a group of two digits ((\d{2})), which will be referenced as $4, followed by
5. a group of two digits ((\d{2})), which will be referenced as $5, followed by
6. a group of two digits ((\d{2})), which will be referenced as $6, followed by
7. an optional group formed by a dot (\.) and 0-to-3 digits (\d{0,3}), which will be referenced as $7

Now we have:

• the year (4 digits) in $1
• the month (2 digits) in $2
• the day (2 digits) in $3
• the hours (2 digits) in $4
• the minutes (2 digits) in $5
• the seconds (2 digits) in $6
• the milliseconds (a dot followed by up to 3 digits) - if present - in $7

and we can use those substrings in the second argument of the String.prototype.replace() function, in order to transform the original string as we need.

For more on RegExp you can refer to: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp

I also find this website useful as a quick reference and to test my RegExp: https://regexr.com/

Answer 2

If the timestring format never changes, you could build your datetime variable like the following:

let timestring = "20221004093142Z"

timestring = 
timestring.substring(0, 4) + "-" + 
timestring.substring(4, 6) + "-" + 
timestring.substring(6, 8) + " " + 
timestring.substring(8, 10) + ":" + 
timestring.substring(10, 12) + ":" + 
timestring.substring(12, timestring.length - 1)

let datetime = new Date(timestring)

console.log(datetime)

You could also build it the same way creating the single year, month etc. values with substring and then set it together.

Pretty sure there is a way to simplify the substring thing with splicing the ":" and "-" chars into the timestring.