Number对象

Number.prototype.toFixed()

toFixed方法先将一个数转为指定位数的小数，然后返回这个小数对应的字符串。

(10).toFixed(2) // "10.00"
10.005.toFixed(2) // Returns "10.01" . Note it rounds up

/**
 * Without parenthesis
 *
 * Uncaught SyntaxError: 
 * Invalid or unexpected token
 */
10.toFixed(2)

Example

12345.6789.toFixed() // Returns '12346': note rounding, no fractional part
12345.6789.toFixed(1) // Returns '12345.7': note rounding
12345.6789.toFixed(6) // Returns '12345.678900': note added zeros
(1.23e+20).toFixed(2) // Returns '123000000000000000000.00'
(1.23e-10).toFixed(2) // Returns '0.00'
2.34.toFixed(1) // Returns '2.3'
2.35.toFixed(1) // Returns '2.4'. Note it rounds up
2.55.toFixed(1) // Returns '2.5'. Note it rounds down - see warning above

-2.34.toFixed(1) // Returns -2.3 (due to operator precedence, negative number literals don't return a string...)

(-2.34).toFixed(1) // Returns '-2.3' (...unless you use parentheses)

参考资料：
JavaScript 标准参考教程（alpha）Number对象
Number.prototype.toFixed()

Array.prototype.sort

const arr = [
  { age: 1 },
  { age: 2 },
  { age: 3 },
  { age: 4 },
  { age: 5 },
  { age: 6 },
  { age: 7 },
  { age: 8 },
  { age: 9 },
  { age: 10 },
  { age: 11 },
  { age: 12 },
  { age: 13 },
  { age: 14 },
  { age: 15 },
  { age: 16 },
  { age: 17 },
  { age: 18 },
  { age: 19 },
  { age: 20 },
  { age: 21 },
  { age: 22 },
  { age: 23 },
  { age: 24 },
  { age: 25 },
  { age: 26 },
  { age: 27 },
  { age: 28 },
  { age: 29 },
  { age: 30 },
  { age: 31 },
  { age: 32 },
  { age: 33 },
  { age: 34 },
  { age: 35 },
  { age: 36 },
  { age: 37 },
  { age: 38 },
  { age: 39 },
  { age: 40 },
  { age: 41 },
  { age: 42 },
  { age: 43 },
  { age: 44 },
  { age: 45 },
  { age: 46 },
  { age: 47 },
  { age: 48 },
  { age: 49 },
  { age: 50 },
  { age: 51 },
  { age: 52 },
  { age: 53 },
  { age: 54 },
  { age: 55 },
  { age: 56 },
  { age: 57 },
  { age: 58 },
  { age: 59 },
  { age: 60 },
  { age: 61 },
  { age: 62 },
  { age: 63 },
  { age: 64 },
  { age: 65 },
  { age: 66 },
  { age: 67 },
  { age: 68 },
  { age: 69 },
  { age: 70 },
  { age: 71 },
  { age: 72 },
  { age: 73 },
  { age: 74 },
  { age: 75 },
  { age: 76 },
  { age: 77 },
  { age: 78 },
  { age: 79 },
  { age: 80 },
  { age: 81 },
  { age: 82 },
  { age: 83 },
  { age: 84 },
  { age: 85 },
  { age: 86 },
  { age: 87 },
  { age: 88 },
  { age: 89 },
  { age: 90 },
  { age: 91 },
  { age: 92 },
  { age: 93 },
  { age: 94 },
  { age: 95 },
  { age: 96 },
  { age: 97 },
  { age: 98 },
  { age: 99 },
  { age: 100 },
  { age: 101 },
  { age: 102 },
  { age: 103 },
  { age: 104 },
  { age: 105 },
  { age: 106 },
  { age: 107 },
  { age: 108 },
  { age: 109 },
  { age: 110 },
  { age: 111 },
  { age: 112 },
  { age: 113 },
  { age: 114 },
  { age: 115 },
  { age: 116 },
  { age: 117 },
  { age: 118 },
  { age: 119 },
  { age: 120 },
  { age: 121 },
  { age: 122 },
  { age: 123 },
  { age: 124 }
];

arr.sort((a, b) => {
  return a.age - b.age;
});