Question

73

Check if a form input exists

rated 0 times [ 79] [ 6] / answers: 1 / hits: 57160 / 12 Years ago, tue, may 15, 2012, 12:00:00

I want to check if an input tag named field2 exists when the user is filling out input name field1. I do that by executing a JavaScript function using the onchange event on field1's input tag. (I'm testing using alert boxes.) If field2 does not exist, JavaScript clicks a button and the form is updated to have both field1 and field2. But the alert box pops up even when field2 exists no matter which of the 3 methods I use. I tried all sorts of combinations using if with null and 'undefined', etc.

Why do the alert boxes pop up if field2 exists ?

function foobar(){



if(!document.getElementsByName(field2){

alert(foobar);

}



if(!document.forms[0].field2){

alert(foobar);

}



if(!document.forms[0].elements.namedItem(field2){

alert(foobar);

}

}

Answers

Only authorized users can answer the question. Please sign in first, or register a free account.

keyanah

Add To Favorites

Follow

Total Points: 642

Total Questions: 93

Total Answers: 114

Location: Virgin Islands (U.S.)

Member since Tue, Jul 7, 2020

4 Years ago

answered 12 Years ago willieelisham · Accepted Answer

Actually, the problem was that the page had various forms and therefore forms[0] was not referring to the form I wanted. So I think the best way is to use this and refer to the input field directly. Also, it is clearer to compare to undefined rather than !.

This works:

function foobar(fooform){

    if (fooform.field2 === undefined) {

        alert(foobar);

    }

}

Called like this:

foobar(this.form);