Are string indexers valid in Javascript?

Question

I ran into a bug that manifested itself in IE8, but not in Firefox, Chrome or IE9+.

A snippet of code:

Date.prototype.ddmmyyyy = function() {
    var yyyy = this.getFullYear().toString();
    var mm = (this.getMonth()+1).toString();
    var dd = this.getDate().toString();
    return (dd[1]?dd:"0"+dd[0]) + '/' + (mm[1]?mm:"0"+mm[0]) + '/' + yyyy;
};

I won't go into details explaining that it does (or tries to) which is blindingly obvious. I wasn't aware that dd[0] and dd[1] would both return undefined in IE8.

What's a better way to write the code? Or is there a way to make the string [/array] indexer work?

Answer 1

You could modify your ternary statement to check the string's length.

dd.length > 1 ? dd : '0' + dd

Answer 2

Use .charAt(1) instead of [1] notation.

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Or you could .split() the strings into Arrays.

var dd = this.getDate().toString().split("");

dd[1];

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Ultimately, I'd do it like this:

Date.prototype.ddmmyyyy = function() {
    var yyyy = this.getFullYear();
    var mm = ("0" + (this.getMonth()+1)).slice(-2);
    var dd = ("0" + this.getDate()).slice(-2);
    return dd + '/' + mm + '/' + yyyy;
};