为什么Array.filter(Number)在JavaScript中过滤掉零? [英] Why does Array.filter(Number) filter zero out in JavaScript?

问题描述

我正在尝试从数组中过滤掉所有非数字元素.使用typeof时，我们可以看到所需的输出.但是使用Number时，它会将零过滤掉.

I'm trying to filter all non-numeric elements out from an array. We can see the desired output when using typeof. But with Number, it filters zero out.

以下是示例(已在Chrome控制台中测试):

Here's the example (tested in Chrome Console):

[-1, 0, 1, 2, 3, 4, Number(0), '', 'test'].filter(Number)
// Which output with zero filtered out:
[-1, 1, 2, 3, 4]  // 0 is filtered

如果我们使用typeof，它不会过滤出预期的零.

If we use typeof, it doesn't filter zero, which was expected.

// code
[-1, 0, 1, 2, 3, 4, Number(0), '', 'test'].filter(n => typeof n === 'number')
// output
[-1, 0, 1, 2, 3, 4, 0]

我的问题:

1. 数字"和类型"方法有什么区别?

1. What is the difference between the 'Number' and 'typeof' approaches?

数字过滤为零，但是数字"本身实际上包含零，这使我感到困惑.

Number filters zero, but 'Number' itself literally contains zero, and this confuses me.

推荐答案

因为0是许多

Because 0 is one of the many falsy values in javascript

所有这些条件将发送到else块:

All these conditions will be sent to else blocks:

if (false)
if (null)
if (undefined)
if (0)
if (NaN)
if ('')
if ("")
if (``)

从 Array.prototype.filter() 文档:

filter()会为数组中的每个元素调用一次提供的callback函数，并为所有值构造一个新数组，所有这些值的回调将返回强制为true的值

filter() calls a provided callback function once for each element in an array, and constructs a new array of all the values for which callback returns a value that coerces to true

在您的情况下，回调函数是Number.因此，您的代码等效于:

In your case the callback function is the Number. So your code is equivalent to:

[-1, 0, 1, 2, 3, 4, Number(0), '', 'test'].filter(a => Number(a)) 

// Number(0) -> 0
// Number(Number(0)) -> 0
// Number('') -> 0
// Number('test') -> NaN

当filter函数选择真实的值(或强制为true)，则返回0和NaN的项目将被忽略.因此，它返回[-1, 1, 2, 3, 4]

When filter function picks truthy values (or values that coerces to true), the items which return 0 and NaN are ignored. So, it returns [-1, 1, 2, 3, 4]

这篇关于为什么Array.filter(Number)在JavaScript中过滤掉零?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！