JavaScript(7)-数値に関する質問

数値タイプ変数と数値オブジェクト変数

var N, n;

N = new Number(123); //      

n = 321;             //      ,       Number     

alert(N); //123

alert(n); //321


 
   

面白いNumbertoString()メソッド

var str, n = 65535;

str = n.toString();

alert(str);           //65535



str = n.toString(2);  //         

alert(str);           //1111111111111111



str = n.toString(8);  //         

alert(str);           //177777



str = n.toString(16); //          

alert(str);           //ffff  



str = n.toString(32); //           (     2-36)

alert(str);           //1vvv


 
   

出力のフォーマット

var str, n = 123456.789;

str = n.toLocaleString(); //     

alert(str);               //123,456,79



str = n.toFixed(0);       //    

alert(str);               //1234567



str = n.toFixed(2);       //2     

alert(str);               //1234567.78



str = n.toExponential(1); //       (1   ),   1     

alert(str);               //1.2e+5



str = n.toExponential(3); //       (1   ),   3     

alert(str);               //1.235e+5



str = n.toPrecision(5);   //  5     

alert(str);               //1.2346e+5



str = n.toPrecision(7);   //  7     

alert(str);               //123456.8 


 
   

ブールから数値

var b = false, n = 123;

n = b + n;

alert(n); //123



b = !b;

n = b + n;

alert(n); //124


 
   

文字列から数値

var n;

n = '111' + 0;    //       

alert(n);         //1110



n = '111' - 0;    //        

alert(n);         //111



alert('111' + 1); //1111

alert('111' - 1); //110


 
   

parseFloat:文字列を浮動小数点数に変換

var num;

num = parseFloat('1.23');

alert(num); //1.23



num = parseFloat('1.23AB456');

alert(num); //1.23



num = parseFloat('-1.23X');

alert(num); //-1.23



num = parseFloat('X1.23X');

alert(num); //NaN (   )



num = parseFloat('');

alert(num); //NaN (   )



num = parseFloat('0xFFFF'); //        ,        0

alert(num); //0



/*              ... */

num = "1.23" - 0;

alert(num); //1.23



/*               ,         parseFloat    ... */

num = "1.23ABC" - 0;

alert(num); //NaN


 
   

parseInt:文字列を整数に変換

var num;

num = parseInt("123ABC");

alert(num); //123



num = parseInt("-123ABC");

alert(num); //-123



num = parseInt("1.23ABC"); //       

alert(num); //1



/*         */

num = parseInt("0xFF"); //       

alert(num); //255



num = parseInt("-0Xff"); //       

alert(num); //-255



/*        ,             */

num = parseInt("1111111111111111", 2);

alert(num); //65535



num = parseInt("FFFF", 16);

alert(num); //65535



num = parseInt("ffff", 16);

alert(num); //65535



num = parseInt("0xffff", 16);

alert(num); //65535



num = parseInt("177777", 8);

alert(num); //65535



num = parseInt("1vvv", 32);

alert(num); //65535



num = parseInt("FFFF", 10);

alert(num); //NaN