小數在JavaScript

Question

如何將該輸出轉換在javascript：

A = 1.0000006

B = 0.00005

C = 2.54695621e-7

的輸出：

a = 1

B = 5E-5

C = 2.547e-7

Answer 1

嘗試以下代碼：

var a = 1.0000006; 
 
var b = 0.00005; 
 
var c = 2.54695621e-7; 
 
var a_Result = Math.round(a); 
 
var b_Result = b.toExponential(); 
 
var c_Result = c.toExponential(3); 
 
console.log(a_Result); 
 
console.log(b_Result); 
 
console.log(c_Result);

Answer 2

利用該輸入：

var nums = [1.0000006, 0.00005, 2.54695621e-7]; 

可以使用Number#toExponential得到指數形式具有一定精度：

function formatNumber(n) { 
    return n.toExponential(3); 
} 

nums.map(formatNumber) 
// ["1.000e+0", "5.000e-5", "2.547e-7"] 

把它分解成有用的部分：

function formatNumber(n) { 
    return n 
     .toExponential(3) 
     .split(/[.e]/); 
} 

nums.map(formatNumber) 
// [["1", "000", "+0"], ["5", "000", "-5"], ["2", "547", "-7"]] 

並修剪掉多餘的：

function formatNumber(n) { 
    var parts = n 
     .toExponential(3) 
     .split(/[.e]/); 

    var integral = parts[0]; 
    var fractional = '.' + parts[1]; 
    var exponent = 'e' + parts[2]; 

    fractional = fractional.replace(/\.?0+$/, ''); 
    exponent = exponent === 'e+0' ? '' : exponent; 

    return integral + fractional + exponent; 
} 

nums.map(formatNumber) 
// ["1", "5e-5", "2.547e-7"] 

ES6：

const formatNumber = n => { 
    const [, integral, fractional, exponent] = 
     /(\d+)(\.\d+)(e.\d+)/.exec(n.toExponential(3)); 

    return integral + 
     fractional.replace(/\.?0+$/, '') + 
     (exponent === 'e+0' ? '' : exponent); 
};