How to judge whether an object is valid?

ellenway

var obj = frame.document.form.text1;
The frame in the above statement is an iframe. When I refresh this iframe, I check obj != false, but obj does not point to the refreshed frame.document.form.text1. How to detect this status?

疯狂的兔子

Use if(obj == frame.document.form.text1)

迪迪安

I feel I should use ===

ellenway

Is obj==null returns fasle not obj != fasle