moment.js reverse .fromNow() - node.js

Question

So i'm working with moment.js.
I see you can translate a date into a human-friendly format using moment().fromNow();
Is there a way to do the opposite?
For example, I want to turn this --> "2 weeks ago" into a normal date format or UNIX timestamp.
I sifted through the documentation but couldnt find anything. Any direction would help, thanks.

Answer 1

Depending on how complicated/different the input strings can be, you could do this:
//parse out the number and the duration
var inputString = "2 weeks ago";
var myRegExp = /^(\d+)\s(\w+)\sago$/;
var results = myRegExp.exec(inputString);
var num = results[1];
var duration = results[2];
moment().subtract(duration,num).toString() //or whatever format you prefer
Note this will work for input strings of the format "number duration ago".
Hope that helps!

Answer 2

In some cases .fromNow() returns string like "30+ days ago". The regex provided in above solution doesn't handle to parse that properly.
Here's the updated regex to handle that case:
var myRegExp = /^(\d+)\+?\s(\w+)\sago$/;

Answer 3

Here is the method that I used to reverse it for the current moment.js locale. I tested it on a few locales and it should work for every locale but it might not.
Change the last two .toString() functions to .valueOf() to get numerical values.
Moment actually doesn't have the week name data for all languages right now, so the function will assume that the string is a week if it could not find the value.
Some languages use translation functions instead of having built in values so the script will not work on those either! If you manually specify your language data then it should work.
//test en locale
moment.locale("en");
console.log(reversefromNow("5 days ago"));
console.log(reversefromNow("in 5 days"));
//test ja locale
moment.locale("ja");
console.log(reversefromNow("5 日前"));
console.log(reversefromNow("5 日後"));
function reversefromNow(input) {
let relativeLocale = JSON.parse(JSON.stringify(moment.localeData()._relativeTime));
let pastfutureObject = {
future: relativeLocale.future,
past: relativeLocale.past
};
delete relativeLocale.future;
delete relativeLocale.past;
//detect if past or future
let pastfuture;
for (const [key, value] of Object.entries(pastfutureObject)) {
if (input.indexOf(value.replace("%s", "")) != -1) {
pastfuture = key;
}
}
//detect the time unit
let unitkey;
for (const [key, value] of Object.entries(relativeLocale)) {
if (input.indexOf(value.replace("%d", "")) != -1) {
unitkey = key.charAt(0);
}
}
//if its not in the data, then assume that it is a week
if (unitkey == null) {
unitkey = "w";
}
const units = {
M: "month",
d: "day",
h: "hour",
m: "minute",
s: "second",
w: "week",
y: "year"
};
//Detect number value
const regex = /(\d+)/g;
let numbervalue = input.match(regex) || [1];
//Add if future, subtract if past
if (pastfuture == "past") {
return moment().subtract(numbervalue, units[unitkey]).valueOf();
} else {
return moment().add(numbervalue, units[unitkey]).valueOf();
}
}