未捕获的TypeError：无法读取未定义的属性“ timing”

Question

How do I properly do object detection for window.performance.timing ?

An unknown version of Chrome being run by Googlebot is spawning the following error:

Uncaught TypeError: Cannot read property 'timing' of undefined

The only instances of window.performance.timing are in the following snippets of code:

else if (
window.performance!=undefined
&& window.performance.timing!=undefined
&& window.performance.timing.toJSON!=undefined) {/* etc */}

Obviously regardless of my efforts to do object detection Googlebot is somehow still spawning the error message. I can not use try and catch and I have zero instances in my JavaScript error log of this happening in any testable (eg Chrome itself) browser, only Googlebot.

Answer 1

Try this way.

else if (
window.performance
&& window.performance.timing
&& window.performance.timing.toJSON) {/* etc */}

And as I know, you should use !== instead of !=

Answer 2

If window.performance is undefined the if statement will still check the other two expressions. If there is no window.performance it can't check for window.performance.timing .

At least that's what I am guessing. I would try to nest the if statements:

if(window.performance != undefined) {
  if(window.performance.timing != undefined) {
    if(window.performance.timing.toJSON != undefined) {
      /* etc */
    }
  }
}

Answer 3

What if window.performance is null ? I bet you would get the same error message.

That's why the canonical way to check objects existence is:

if (window.performance && window.performance.whatever && ...) ...