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问题:

What are cons of force a web site viewed in IE to compatible mode? Say we force IE9 to IE8 compatiblity mode?

Performance drawbacks
Can't use any new IE9 specific features like HTML5/CSS3/SVG

Why?

We run legacy web app which is developed since 2000 so it's a mess ball fighting to be compatible with Chrome, Opera, Firefox, IE6/7/8 and now we decide to add IE9 to the list. But with IE9 we run in issues with printing, "Permission deniend" JavaScript errors (probably something about cross-frame JavaScript calls) and next issues - the easy workaround is to force IE9 to behave as a IE8 and then everything works fine. But I am still not sure if it's way to go...

回答1:

first our app is public site (for our clients)

You have a public website developed in 2000 and it doesn't work on modern browsers? Deprecate it or re-write it.

Don't hack your code to support modern browsers, the website is clearly poorly written and doesn't apply to standards. You can't get away with this.

The only place where you can get away with this level of incompatibility is intranet applications and even then you should simply state "it works on browser X, live with it"

You can't say that to public facing clients. I mean you can try, but have fun losing business to your competitors.

Re-develop your website to match the W3C HTML/CSS standards and the ES5 standards and it will be completely future facing (for some years).

Alas, the way the web works is that anything more then 5 years old is deprecated. So either re-write it every 5 years or get out of the web business.

In terms of actually using compatibility mode, don't. IE6-8 are horrible engines and should be avoided like the plague. If you use them then you can't write future facing standards compliant code.

Your code needs to match the standards and you should fix / shim / patch any browser specific bugs where those browsers don't implement the standards.

回答2:

You cannot say you have tested in IE6/7/8/9 until you have tested in those different versions. Emulating the test environment is not the same as using the test environment. To my knowledge IE7/8 compatibility modes are the older render engines, not the underlying browser as a whole, bugs and all. It is closed source so you will never know.

Convert Microsoft's free to download virtual disk images for cross-browser testing to Virtualbox images and put them on a machine that just runs Virtualbox. An old machine will do, run the VMs headless and access them with remote desktop. In that way you will be able to test in all browsers without burdening your machine with MS/Spyware.

回答3:

I believe your system admins can set IE to compatibility mode for all intranet traffic using the Group Policy Editor. Any site you create will from this point forward, you can add a meta tag to force IE9 to render natively and use all the newer features...

I'm having to do that on my current project using the following doctype and meta tag in my header:

<!DOCTYPE HTML >

<meta http-equiv="X-UA-Compatible" content="IE=100" />

回答4:

Compatability mode is something that MS introduced to give people some chance to upgrade their applications, not for long term use. AFAIU.

If you want your application to be compatible with IE9, then you will have to change it. If you are trying to maintain IE6-9 compatibility then you have a real challenge, and you should consider whether this is really practical - in essence, you need at least 2 distinct sets of html. Is this practical for you?

IE9 compatibility mode is different form IE9 and IE8 - it draws bits from both. So you need to do a full test agaisnt the compatibility mode version, and ensure that it remains working against this.

So in answer to the question, the cons are that you are not being IE9 compatible, and there is a danger that when IE10 comes out, your code will not run against that in any mode. You are putting the effort into compatibilty testing without providing for future changes. You would do better, in the longer term, to make your code IE9 compatible. Also, the message you are giving your clients is that your code base is not going to be compatible for much longer. Unless you are talking to them about a re-work, this is a real negative.

However, it sounds like your entire code needs a re-work, to forget about IE6 and be written for modern working browsers. Using compatibility mode until that happens is probably OK. If you do this - and tell your clients - then staying in compatibility mode is viable.

回答5:

Using compatibility mode will NOT cause the browser to use the JavaScript engine that was present in the old version of IE.

By that I mean it will run any JavaScript code using the IE9 engine. Which was a problem for us when debugging an old product that had a problem with IE7/8.