How to parse a date in format "YYYYmmdd" in JavaScript?

Question

This is a noob question:

How to parse a date in format "YYYYmmdd" without external libraries ? If the input string is not in this format I would like to get invalid Date (or undefined if it will be easier).

Answer 1

function parse(str) {     if(!/^(\d){8}$/.test(str)) return "invalid date";     var y = str.substr(0,4),         m = str.substr(4,2),         d = str.substr(6,2);     return new Date(y,m,d); } 

Usage:

parse('20120401'); 

UPDATE:

As Rocket said, months are 0-based in js...use this if month's aren't 0-based in your string

function parse(str) {     if(!/^(\d){8}$/.test(str)) return "invalid date";     var y = str.substr(0,4),         m = str.substr(4,2) - 1,         d = str.substr(6,2);     return new Date(y,m,d); } 

UPDATE:

More rigorous checking for validity of date. Adopted HBP's way to validate date.

function parse(str) {     var y = str.substr(0,4),         m = str.substr(4,2) - 1,         d = str.substr(6,2);     var D = new Date(y,m,d);     return (D.getFullYear() == y && D.getMonth() == m && D.getDate() == d) ? D : 'invalid date'; } 

Answer 2

A more robust version validating the numbers :

 function parse (str) {         // validate year as 4 digits, month as 01-12, and day as 01-31          if ((str = str.match (/^(\d{4})(0[1-9]|1[0-2])(0[1-9]|[12]\d|3[01])$/))) {            // make a date            str[0] = new Date (+str[1], +str[2] - 1, +str[3]);            // check if month stayed the same (ie that day number is valid)            if (str[0].getMonth () === +str[2] - 1)               return str[0];         }         return undefined;  } 

See fiddle at : http://jsfiddle.net/jstoolsmith/zJ7dM/

I recently wrote a much more capable version you can find here : http://jsfiddle.net/jstoolsmith/Db3JM/