how to tell if a variable is a reference to an HTML Element"<select>"?

[Zhang Weiwu]

Dear all

How does javascript realiablily tell if a variable is a reference to an
HTML Element "<select>", without causing browser to pop up error message?

if (variable.constructor == HTMLElementSelect)
// doesn't work, Firefox complain no such property if variable is undefined

if (typeof variable == "object" && variable.constructor == HTMLElementSelect)
// doesn't work, IE complain object do not have this property "constructor"
// However, IE do show constructor of objects if it's not Element Object

if (variable.tagName == "select")
// doesn't work if variable is undefined.

if (typeof variable == "object" && variable.tagName == "select")
// doesn't work, complain property do not exist if object is an non DOM Node

if (typeof variable == "object" && variable.tagName && variable.tagName == "select")
// must the working solution be this complicated?

Thanks, sorry I didn't read other people's code enough to have seen how
tho handle this neatly. And I didn't google out either.

 

[lucas.e.smith]

Dear all

How does javascript realiablily tell if a variable is a reference to an
HTML Element "<select>", without causing browser to pop up error message?

if (variable.constructor == HTMLElementSelect)
// doesn't work, Firefox complain no such property if variable is undefined

if (typeof variable == "object" && variable.constructor == HTMLElementSelect)
// doesn't work, IE complain object do not have this property "constructor"
// However, IE do show constructor of objects if it's not Element Object

if (variable.tagName == "select")
// doesn't work if variable is undefined.

if (typeof variable == "object" && variable.tagName == "select")
// doesn't work, complain property do not exist if object is an non DOM Node

if (typeof variable == "object" && variable.tagName && variable.tagName == "select")
// must the working solution be this complicated?

Thanks, sorry I didn't read other people's code enough to have seen how
tho handle this neatly. And I didn't google out either.

if (variable && typeof(variable.nodeName) !== 'undefined' &&
variable.nodeName === 'SELECT') {
...
}

 

[scripts.contact]

Dear all

How does javascript realiablily tell if a variable is a reference to an
HTML Element "<select>", without causing browser to pop up error message?

if(variable && (varibale instanceof HTMLSelectElement) )
alert("variable is a select element")

 

[Zhang Weiwu]

于 Fri, 06 Jul 2007 10:24:45 -0700，scripts.contact写到：

if(variable && (varibale instanceof HTMLSelectElement) )
alert("variable is a select element")

"Error: HTMLSelectElement undefined.", says IE6 politely.

 

[Zhang Weiwu]

于 Fri, 06 Jul 2007 08:51:10 -0700，lucas.e.smith写到：

if (variable && typeof(variable.nodeName) !== 'undefined' &&
variable.nodeName === 'SELECT') {
...
}

Thank you, this works for both IE and Firefox. Just as I thought, with IE
usually there is no simple way.

 

[The Natural Philosopher]

于 Fri, 06 Jul 2007 08:51:10 -0700，lucas.e.smith写到：


Thank you, this works for both IE and Firefox. Just as I thought, with IE
usually there is no simple way.

As an aside, what is the meaning of '!==' and '===' ?

 

[The Natural Philosopher]

The Natural Philosopher said the following on 7/8/2007 4:12 PM:



!== means it is NOT an exact match.
=== means it is an exact match.

And "match" includes the constructor and all. The undefined and null ==
another but they are not === to one another. The major difference, to me
(and easiest way for me to keep up with it) is that == does a type
conversion and === does not. The ! simply means NOT.

TVM!