//小结
// toExponential 保留小数点( 0-20 bit )

    document.writeln(Math.PI.toExponential(0)); //3e+0

    document.writeln(Math.PI.toExponential(2)); //3.14e+0

    document.writeln(Math.PI.toExponential(4)); //3.1416e+0

    document.writeln(Math.PI.toExponential(7)); //3.1415927e+0

// toFixed 换成十进制后 保留小数点( 0-20 bit )

    document.writeln(Math.PI.toFixed(0));

    document.writeln(Math.PI.toFixed(2));

    document.writeln(Math.PI.toFixed(4));

    document.writeln(Math.PI.toFixed(7)); //3.1415927

// toPrecision 换成十进制后 保留小数点( 1-21 bit )

    document.writeln(Math.PI.toPrecision(1)); //3

    document.writeln(Math.PI.toPrecision(2)); //3.1

    document.writeln(Math.PI.toPrecision(4)); //3.142

    document.writeln(Math.PI.toPrecision(7)); //3.141593

// toString(radix) radix是基数 默认为10 换成十进制后 保留小数点( 2-36 bit )

    document.writeln(Math.PI.toString(2)); //11.001001000011111101101010100010001000010110100011

    document.writeln(Math.PI.toString(8)); //3.1103755242102643

    document.writeln(Math.PI.toString(16)); //3.243f6a8885a3

    document.writeln(Math.PI.toString()); //3.141592653589793