[Javascript] substr() & substring()

w3c substr()的解釋:
Extracts the characters from a string, beginning at a specified start position, and through the specified number of character.
簡單的講就是，指定開始位置與需要的長度抽取出子字串。index從0開始。

語法:
"somestring".substr(start, length)

例子:
alert("12345".substr(2,3)); //會印出345

w3c substring()的解釋:
Extracts the characters from a string, between two specified indices.
substring()則是抽取出兩個index之間的子字串。index從0開始。

語法:
"something".substring(from, to)

例子:
alert("12345".substring(2,3)); //會印出3