javascript(substr與substring)

還有一點差別是百度經驗上沒有說到的，這裡      

var test = "hello";      

var a = "";      

a = test.substring(0,3); a=hel      

a = test.substr(0,3);  a=hel      
    
a = test.substring(1,3); a=el      
    
a = test.substr(1,3);  a=ell