Javascript study notes -- datatype and values

Code
VaR Str =   " Zhuobin " ;
VaR Last_char = Str. charat (Str. Length - 1 ); // ---- N
VaR Sub = Str. substring ( 0 , 4 ); // -- Zhuo
VaR I = Str. indexof ( ' Z ' ); // -- 0
2 . Converting number to string
Number are automatically to string when need.
Number + String = String
Number +   ""   = String
  VaR _ String = String (number );
Another way:
  VaR _ String = Number. tostring ();
  VaR N =   17 ;
2_string = N. tostring ( 2 ); // -- 10001
8_string = N. tostring ( 8 ); // -- 021
16_string = N. tostring ( 16 ); // -- 0x11
  //
VaR N =   123456.789 \
N. tofixed ( 0 ); // 123457
N. tofixed ( 2 ); // -- 123456.79
N. toexponential ( 1 ); // 1.2e + 5
N. toexponential ( 3 ); // 1.23 // exponential Representation
N. toprecision ( 4 ); // 1.235e + 5 // rounding
N. toprecision ( 7 ); // 123456.8