Fix bug: on ie 7 & 8, isAppeared function didn't work.
Fix bug: on ie 7 & 8, isAppeared function didn't work.

Ju2ender/JavaScript-E,Ju2ender/JavaScript-Exercise,Ju2ender/JavaScript-E,Ju2ender/JavaScript-Exercise,Ju2ender/JavaScript-Exercise,Ju2ender/JavaScript-Exercise,Ju2ender/JavaScript-E,Ju2ender/JavaScript-E