Cannot read property from my document.forms

Question

i have this js code on my page:

var mail = 'idEmail';
value(mail);
//function returning the value of an input
function value(input){
  return eval('window.document.Search.'+input).value;
}

I have this error:

TypeError: Cannot read property 'idEmail' of undefined

Why when i change return eval('window.document.Search.'+input).value; by return eval('window.document.forms['Search'].'+input).value; it's work?

document.forms["general"]
or
document.forms[0]
or
document.general

it's the same

Oh for crying out loud, do away with the `eval` nonsense ... https://stackoverflow.com/questions/4244896/dynamically-access-object-property-using-variable — CBroe, Aug 03 '17 at 09:30

Robby Cornelissen · Answer 1 · 2017-08-03T09:32:14.357

1

Because you forgot the forms part:

return eval('window.document.forms.Search.'+input).value;

Note that eval is evil. You might as well do:

return document.forms.Search[input].value;

edited Aug 03 '17 at 09:32

answered Aug 03 '17 at 09:30

Robby Cornelissen

91,784
22
134
156

1

`return document.forms.Search[input].value;` – Niet the Dark Absol Aug 03 '17 at 09:31
2

this is why eval is evil [Why is using the JavaScript eval function a bad idea?](https://stackoverflow.com/questions/86513/why-is-using-the-javascript-eval-function-a-bad-idea) – Liam Aug 03 '17 at 09:31

score 1 · Answer 2 · answered Aug 03 '17 at 09:31

In your function you are trying to access a property of an undefined object, in fact .Search isn't a property of window.document but of window.document.forms instead, change it like this:

function value(input){
  return window.document.forms.Search[input].value;
}

Note:

It's better to avoid using eval, you can get rid of it in your function.

Cannot read property from my document.forms

2 Answers2