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Editorial Team
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Asked: 2026-05-31T18:52:53+00:00

The last log in the following code doesn’t work in Firefox. Why? (function() {

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The last log in the following code doesn’t work in Firefox. Why?

(function() {

    String.prototype.toDate = function() {
        return new Date(this);
    };

    console.log(Date.parse("2012-01-31"));
    console.log(new Date("2012-01-31"));
    console.log("2012-01-31".toDate());

})();

To test this in a browser, I put the snippet above into a file and used the following HTML.

<!DOCTYPE html>
<body>
    <script src="wtf.js"></script>
</body>

NodeJS (v0.4.12):

1327932000000
Mon, 30 Jan 2012 14:00:00 GMT 
Mon, 30 Jan 2012 14:00:00 GMT

Chrome (17.0.963.79):

1327968000000
Tue Jan 31 2012 10:00:00 GMT+1000 (EST)
Tue Jan 31 2012 10:00:00 GMT+1000 (EST)

Firefox (10.0):

1327968000000
Date {Tue Jan 31 2012 10:00:00 GMT+1000 (EST)}
Date {Invalid Date}
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1 Answer

  1. Editorial Team

    this in Firefox’s String.prototype appears to not reference the string, as a string. If you add to your method:

    String.prototype.toDate = function() {
        return new Date(String(this));
    };

    it works alright.

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