FOR loop and string concatenating with JavaScript gives me an undefined value

Question

I have the array

var data = [name, address, city, country];

And the loop

var columns;
for (var i = 0; i < data.length; i++) {
    columns += "data[" + i + "], ";
}
columns = columns.slice(0, -2);
alert(columns);

The alert message says

undefineddata[0], data[1], data[2], data[3]

What am I doing wrong here? I want to remove the undefined...

Nick Craver · Accepted Answer · 2010-10-22 00:08:31Z

17

You need to start with an empty string, like this:

var columns = "";

Right now what you have is basically equivalent to:

var columns = undefined;

Which when concatenated to a string, gives you "undefined".

answered Oct 22, 2010 at 0:08

Nick Craver

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