转换为驼峰命名法

var s1 = "get-element-by-id"; 给定这样一个连字符串，写一个function转换为驼峰命名法形式的字符串 getElementById

First Tab

1. 匹配 ' - '

2. 对后面的首字母大写

Second Tab

replace 的语法

str.replace(regexp|substr, newSubstr|function)

其中function 的回调参数有

match	The matched substring. (Corresponds to $& above.)
p1, p2, ...	The nth string found by a parenthesized capture group, provided the first argument to replace() was a RegExp object. (Corresponds to $1, $2, etc. above.) For example, if /(\a+)(\b+)/, was given, p1 is the match for \a+, and p2 for \b+.
offset	The offset of the matched substring within the whole string being examined. (For example, if the whole string was 'abcd', and the matched substring was 'bc', then this argument will be 1.)
string	The whole string being examined.