Difference between function substring() and substr()

1.subsring()

Grammar: stringObject.substring(start,stop). This function is used to extract string between the two characters of the specified index.It needs one or two parameters.

The parameter stop is not necessary.

stringObject.substring(start)
    "abcdefg".substring()//cdefg
           

stringObject.substring(start,stop)
    "abcdefg".substring(,)//cd
           

Example: let sring “abcd” become “cdab”?

"abcd".substring(2)+"abcd".substring(0,2)//cdab
           

2.substr()

Grammar: stringObject.substr(start,length). This function is also used to extract string and the parameter length specifies the length of the string.

The parameter length is not necessary. If funciton does not take this parameter,it works as well as substring().

stringObject.substr(start)
    "abcdefg".substr()//cdefg
           

stringObject.substring(start,length)
    "abcdefg".substr(,)//cdef
           

3.Conclusion：

When the two function both take one parameter.they have same function.When take two,the second parameter of substring() represents position index,and length of substr().