Cannot Read Property 'Elements' of Undefined - in JS Console

Question

HTML form (outputed thru PHP)

$retVal .= "<form id= 'importSampleDataForm' name = 'importSampleDataForm' onsubmit = \"return false\" >\n";

    // Form content edited out; it contains several dozen checkboxes

$retVal .= sprintf("<input type='button' class='wn_button' onclick='SaveMotorSkills();' value='Import Selected'>\n");
$retVal .= "</form>\n";

JavaScript / Ajax

function SaveMotorSkills() // {{{
{
    // {{{ Ajax Header
    var httpRequest = CreateHttpRequest();
    if (!httpRequest) { 
        DialogFail('AJAX initialization error. ', 1 );
        return false; 
    } // }}}

    var params = '_SaveMotorSkills=1';
    for(i=0; i<document.importSampleDataForm.elements.length; i++) // line with error
    {
        params += "&" + document.importSampleDataForm.elements[i].name + 
            "=" + document.importSampleDataForm.elements[i].value ;
    }

    // edit out AJAX setup

    httpRequest.send(params);
    DialogSave("Saving...");
} // }}}

See "Line With Error Above" in for loop. JS Console says

Uncaught TypeError: Cannot read property 'elements' of undefined

I have looked at this code so much my eyes can't take it anymore. Does anyone else see anything I don't? I can add more code if needed.

Solution

Try

document.getElementById('importSampleDataForm').elements.length

Also, nested forms are not allowed, so that also needs to be resolved.

Comments

[Nahydrin]

Are you running the function SaveMotorSkills from the footer, or after the page/html is on the screen? You should be.

[TheLettuceMaster]

It is run from a separate .js document and the form is already displayed on the screen. When you click the button on bottom of form, this is when it is ran.

[TheLettuceMaster]

that gives me new error: Uncaught TypeError: Cannot read property 'elements' of null

[Patrick]

@KickingLettuce, When does SaveMotorSkills run? The new error is still on the same line, right?

[TheLettuceMaster]

I added this answer above in comments.

[Patrick]

Are you in Chrome? Try this: 1) load up web page. 2) press F12 3) click Console 4) run document.getElementById('importSampleDataForm').elements.len‌​gth; and see what that gives you there.

[TheLettuceMaster]

It says same thing as my first comment; 'null'

[Patrick]

Try just document.getElementById('importSampleDataForm'); maybe the html code isn't appearing on the page.

[TheLettuceMaster]

That says null as well. When I inspect element; the correct form is there with the correct id/name. The script isn't being ran until AFTER page has been loaded and then only if button is clicked.

[TheLettuceMaster]

I just noticed, this form is inside a form; would that cause the issue? I removed the inner form and used the name of the outer form, now it seems to find it.

[Patrick]

You got it. Nested forms are not allowed, stackoverflow.com/questions/379610/can-you-nest-html-forms

[TheLettuceMaster]

You can add that as your answer and I will select.