如何查看是否可以访问window.opener？

Question

How can I check if I have access to window.opener?

I'm getting an error if I open my page in a new window from a file that is not connected with my page ( access denied ).

Code:

if (window.opener) {
        if (window.opener.document.getElementById('myHidden') !== "undefined") {
            if (window.opener.document.getElementById('myHidden').value == "1" && $("#inputXYZ").val() != "1") {

In line 2 the error occurs. But only if I open the page from a random page (that of course does not have an input field called "myHidden"). If I open the page from a "valid" page that has such an element, it is working.

Answer 1

You're comparing an element instance with the string "undefined" , and you're not checking whether window.opener.document is present (I don't know whether you have to or not, but it's easy to add). You probably meant:

// Note: Still not right, see below
if (typeof window.opener.document.getElementById('myHidden') !== "undefined")

...except that that's still not correct, because getElementById returns null (not undefined ) when there's no matching element.

Here's how I'd do it:

var input = window.opener &&
            window.opener.document &&
            window.opener.document.getElementById('myHidden');
var value = input && input.value;
if (value != "1") {
    // Do something
}

That uses the curiously powerful && operator (close cousin to the curiously-powerful || operator ). The first assignment will short-circuit if window.opener or window.opener.document is "falsey" ( null or undefined or 0 or "" or NaN or, of course, false -- and those last four don't apply), resulting in input being undefined . The second assignment will short-circuit if input is falsey, resulting in value being undefined . undefined != "1" , so...

Answer 2

Check if you have access to window.opener.document:

if (window.opener && window.opener.document) {
        if (window.opener.document.getElementById('myHidden') !== "undefined") {
                if (window.opener.document.getElementById('myHidden').value == "1" && $("#inputXYZ").val() != "1") {
                }
        }
}

And if you want to be really sure add in a check for window.opener.document.getElementById eg

if (window.opener && window.opener.document && window.opener.document.getElementById) {
        if (window.opener.document.getElementById('myHidden') !== "undefined") {
                if (window.opener.document.getElementById('myHidden').value == "1" && $("#inputXYZ").val() != "1") {
                }
        }
}