Why is JS variable undefined?

Question

This is strange - I must be missing something! I have this simple js thing that goes like this;

<select onchange='my_function(this.options[this.selectedIndex].value),\"my_text\"'>

and the JS is simply;

function my_function(selected, text) {
    var link="file.php?var1="+selected+"&var2="+text;
    document.write(link);
}

But I keep getting link=file.php?var1=selected&var2=undefined

I have an almost identical function which works fine!

It would be helpful to repro this in a jsfiddle.net and link to that fiddle here — Dan Esparza
– Dan Esparza, Commented Oct 4, 2013 at 18:23

Joshua Dwire · Accepted Answer · 2013-10-04 18:30:40Z

2

Your select html should be this instead:

<select onchange="my_function(this.options[this.selectedIndex].value,'my_text')">

You were closing your function call too early. Also, note that I've switched the outer quotes to be double and the inner quotes to be single. You don't need to escape the inside quotes, and it's more conventional for attributes to be double quoted instead of single quoted..

edited Oct 4, 2013 at 18:30

answered Oct 4, 2013 at 18:22

Joshua Dwire

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1 Comment

tjohnson_nb Over a year ago

Actually, it was simply the misplaced bracket :( - thanks for your help!

David · Accepted Answer · 2013-10-04 18:31:38Z

1

You're not passing the second value to the function. It's outside of the function call (and acting only as invalid markup). Try:

<select onchange="my_function(this.options[this.selectedIndex].value, 'my_text')">

I changed two things here:

Moved the my_text value into the function call.
Changed the quotes. HTML expects double-quotes, JavaScript can use either single-quotes or double-quotes. So it's clearer to use double-quotes for the HTML markup and single-quotes in the inline JavaScript in this case.

answered Oct 4, 2013 at 18:31

David

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Comments

Zaheer Ahmed · Accepted Answer · 2013-10-04 18:26:40Z

0

replace:

<select onchange='my_function(this.options[this.selectedIndex].value),\"my_text\"'>

with this:

<select onchange='my_function(this.options[this.selectedIndex].value),"my_text"'>

because \ is a escape character, and it causing to pass your text as my_text instead of "my_text" and in first one is not the correct string.

I think you try to add " quotation over the string, but query string is by default a string you no need to add quotation if still you needs then try:

<select onchange='my_function(this.options[this.selectedIndex].value),"\"my_text\""'>

answered Oct 4, 2013 at 18:26

Zaheer Ahmed

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