Converting a string to a date in JavaScript
How can I convert a string to a date in JavaScript?
var st = "date in some format"
var dt = new date();
var dt_st= //st in date format same as dt
Answers:
var a = "13:15"
var b = toDate(a, "h:m")
//alert(b);
document.write(b);
function toDate(dStr, format) {
var now = new Date();
if (format == "h:m") {
now.setHours(dStr.substr(0, dStr.indexOf(":")));
now.setMinutes(dStr.substr(dStr.indexOf(":") + 1));
now.setSeconds(0);
return now;
} else
return "Invalid Format";
}Performance
Today (2020.05.08) I perform tests for chosen solutions - for two cases: input date is ISO8601 string (Ad,Bd,Cd,Dd,Ed) and input date is timestamp (At, Ct, Dt). Solutions Bd,Cd,Ct not return js Date object as results, but I add them because they can be useful but I not compare them with valid solutions. This results can be useful for massive date parsing.
Conclusions
- Solution
new Date(Ad) is 50-100x faster than moment.js (Dd) for all browsers for ISO date and timestamp - Solution
new Date(Ad) is ~10x faster thanparseDate(Ed) - Solution
Date.parse(Bd) is fastest if wee need to get timestamp from ISO date on all browsers
Details
I perform test on MacOs High Sierra 10.13.6 on Chrome 81.0, Safari 13.1, Firefox 75.0. Solution parseDate (Ed) use new Date(0) and manually set UTC date components.
let ds = '2020-05-14T00:00Z'; // Valid ISO8601 UTC date
let ts = +'1589328000000'; // timestamp
let Ad = new Date(ds);
let Bd = Date.parse(ds);
let Cd = moment(ds);
let Dd = moment(ds).toDate();
let Ed = parseDate(ds);
let At = new Date(ts);
let Ct = moment(ts);
let Dt = moment(ts).toDate();
log = (n,d) => console.log(`${n}: ${+d} ${d}`);
console.log('from date string:', ds)
log('Ad', Ad);
log('Bd', Bd);
log('Cd', Cd);
log('Dd', Dd);
log('Ed', Ed);
console.log('from timestamp:', ts)
log('At', At);
log('Ct', Ct);
log('Dt', Dt);
function parseDate(dateStr) {
let [year,month,day] = dateStr.split(' ')[0].split('-');
let d=new Date(0);
d.setUTCFullYear(year);
d.setUTCMonth(month-1);
d.setUTCDate(day)
return d;
}<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.19.1/moment-with-locales.min.js"></script>
This snippet only presents used soultions Results for chrome
