Substring issue

[Toly]

C# Substring method takes start index + length (http://msdn.microsoft.com/en-us/library/aka44szs%28v=vs.110%29.aspx)
It gets translated to JS substring method that takes start index + end index (http://www.w3schools.com/jsref/jsref_substring.asp)

Instead shouldn't it be translated to substr method(http://www.w3schools.com/jsref/jsref_substr.asp)? It takes same parameters as C#.