price === NaN 永远是个false

[BarleyBig]

js中 NaN!==NaN

[luckyadam]

所以文档标注这个写法是错的

[js-newbee]

那么 price !== NaN 不也永远是 true 么... 感觉文档没毛病

[Garfield550]

先说观点：我也觉得原文档没毛病，所以这个修改是不必要的。

理由：

1. MDN 文档关于 NaN 的判断方式已经说得很清楚了：

NaN compares unequal (via ==, !=, ===, and !==) to any other value -- including to another NaN value. Use Number.isNaN() or isNaN() to most clearly determine whether a value is NaN. Or perform a self-comparison: NaN, and only NaN, will compare unequal to itself.

2. 我对于提交者写的 NaN !== NaN 的作用意义不明。

3. 我个人对 NaN 的理解也不是很清晰，写了以下断言做了测试，发现 NaN !== NaN 没什么意义，断言全部 PASS：

console.assert(NaN === NaN, 'ASSERT: NaN equals NaN'); // Assertion failed: ASSERT: NaN equals NaN
console.assert(Number.NaN === NaN, 'ASSERT: Number.NaN equals NaN'); // Assertion failed: ASSERT: Number.NaN equals NaN
console.assert('NotANumber' === NaN, 'ASSERT: String NotANumber equals NaN'); // Assertion failed: ASSERT: String NotANumber equals NaN
console.assert('1' === NaN, 'ASSERT: String 1 equals NaN'); // Assertion failed: ASSERT: String 1 equals NaN
console.assert(1 === NaN, 'ASSERT: Number 1 equals NaN'); // Assertion failed: ASSERT: Number 1 equals NaN
console.assert(Infinity === NaN, 'ASSERT: Infinity equals NaN'); // Assertion failed: ASSERT: Infinity equals NaN
console.assert(true === NaN, 'ASSERT: Boolean true equals NaN'); // Assertion failed: ASSERT: Boolean true equals NaN
console.assert(false === NaN, 'ASSERT: Boolean false equals NaN'); // Assertion failed: ASSERT: Boolean false equals NaN
console.assert(null === NaN, 'ASSERT: Null equals NaN'); // Assertion failed: ASSERT: Null equals NaN
console.assert(undefined === NaN, 'ASSERT: Undefined equals NaN'); // Assertion failed: ASSERT: Undefined equals NaN

console.assert(NaN !== NaN, 'ASSERT: NaN not equal NaN'); // PASS
console.assert(Number.NaN !== NaN, 'ASSERT: Number.NaN not equal NaN'); // PASS
console.assert('NotANumber' !== NaN, 'ASSERT: String NotANumber not equal NaN'); // PASS
console.assert('1' !== NaN, 'ASSERT: String 1 not equal NaN'); // PASS
console.assert(1 !== NaN, 'ASSERT: Number 1 not equal NaN'); // PASS
console.assert(Infinity !== NaN, 'ASSERT: Infinity not equal NaN'); // PASS
console.assert(true !== NaN, 'ASSERT: Boolean true not equal NaN'); // PASS
console.assert(false !== NaN, 'ASSERT: Boolean false not equal NaN'); // PASS
console.assert(null !== NaN, 'ASSERT: Null not equal NaN'); // PASS
console.assert(undefined !== NaN, 'ASSERT: Undefined not equal NaN'); // PASS

console.assert(isNaN(NaN), 'ASSERT: isNaN(NaN)'); // PASS
console.assert(isNaN(Number.NaN), 'ASSERT: isNaN(Number.NaN)'); // PASS
console.assert(isNaN('NotANumber'), `ASSERT: isNaN('NotANumber')`); // PASS
console.assert(isNaN('1'), `ASSERT: isNaN('1')`); // Assertion failed: ASSERT: isNaN('1')
console.assert(isNaN(1), 'ASSERT: isNaN(1)'); // Assertion failed: ASSERT: isNaN(1)
console.assert(isNaN(Infinity), 'ASSERT: isNaN(Infinity)'); // Assertion failed: ASSERT: isNaN(Infinity)
console.assert(isNaN(true), 'ASSERT: isNaN(true)'); // Assertion failed: ASSERT: isNaN(true)
console.assert(isNaN(false), 'ASSERT: isNaN(false)'); // Assertion failed: ASSERT: isNaN(false)
console.assert(isNaN(null), 'ASSERT: isNaN(null)'); // Assertion failed: ASSERT: isNaN(null)
console.assert(isNaN(undefined), 'ASSERT: isNaN(undefined)'); // PASS

console.assert(Number.isNaN(NaN), 'ASSERT: Number.isNaN(NaN)'); // PASS
console.assert(Number.isNaN(Number.NaN), 'ASSERT: Number.isNaN(Number.NaN)'); // PASS
console.assert(Number.isNaN('NotANumber'), `ASSERT: Number.isNaN('NotANumber')`); // Assertion failed: ASSERT: Number.isNaN('NotANumber')
console.assert(Number.isNaN('1'), `ASSERT: Number.isNaN('1')`); // Assertion failed: ASSERT: Number.isNaN('1')
console.assert(Number.isNaN(1), 'ASSERT: Number.isNaN(1)'); // Assertion failed: ASSERT: Number.isNaN(1)
console.assert(Number.isNaN(Infinity), 'ASSERT: Number.isNaN(Infinity)'); // Assertion failed: ASSERT: Number.isNaN(Infinity)
console.assert(Number.isNaN(true), 'ASSERT: Number.isNaN(true)'); // Assertion failed: ASSERT: Number.isNaN(true)
console.assert(Number.isNaN(false), 'ASSERT: Number.isNaN(false)'); // Assertion failed: ASSERT: Number.isNaN(false)
console.assert(Number.isNaN(null), 'ASSERT: Number.isNaN(null)'); // Assertion failed: ASSERT: Number.isNaN(null)
console.assert(Number.isNaN(undefined), 'ASSERT: Number.isNaN(undefined)'); // Assertion failed: ASSERT: Number.isNaN(undefined)