提取外部javascript查询字符串/锚点值：file.js #foo = bar(Extract external javascript query string/anchor value: file.js#foo=bar)

 看看你的if语句。 如果滚动大于或等于850，则检查它是否小于或等于650 ??? 
 
 这是非常基本的if语句，仍然不确定你想要实现什么，那么我只能推荐这个 
 
if(scroll >= 850){
    //Larger or Equal to 850    
} else if(scroll >= 650){
    //More than or equal to 650 LESS than 850
} else if(scroll >= 450) {
    //More than or equal to 450 LESS than 650
}.. BLAH BLAH.... else { };
 
 这有意义吗？ 看到这个小提琴 

Look at your if statement. If scroll is bigger or equal to 850 then check if it's less than or equal to 650??? 
 
This is very basic if statements, still unsure of exactly what you want to achieve then I can only recommend this 
 
if(scroll >= 850){
    //Larger or Equal to 850    
} else if(scroll >= 650){
    //More than or equal to 650 LESS than 850
} else if(scroll >= 450) {
    //More than or equal to 450 LESS than 650
}.. BLAH BLAH.... else { };
 
Does this make sense? See this fiddle