使用“布尔"作为 JavaScript 中 .filter() 的参数

Using quot;Booleanquot; as the argument to .filter() in JavaScript(使用“布尔作为 JavaScript 中 .filter() 的参数)

问题描述

最近了解到可以使用Boolean关键字来判断一个布尔值是否为false，例如

Recently I've learned that you can use the Boolean keyword to check whether a boolean value is false, e.g.

    function countSheeps(arrayOfSheeps) {
          return arrayOfSheeps.filter(Boolean).length;
    }

arrayOfSheeps 只是一个布尔值数组.由于我一直无法找到有关使用布尔"作为关键字的任何信息，我想知道这个词是否还有其他用途，或者甚至只是我可以用来了解它的任何资源.

Where the arrayOfSheeps is simply an array of boolean values. As I've been unable to find anything about using 'Boolean' as a keyword, I was wondering if there are any other uses for the word, or even just any resources I can use to learn about it.

推荐答案

Boolean 不是关键字，它是 function，而函数只是对象，可以传递.同理:

Boolean is not a keyword, it is a function, and functions are just objects, that you can pass around. It is the same as:

return arrayOfSheeps.filter(function(x){return Boolean(x)}).length;

由于 function(x){return f(x)} === f 那么你可以简化:

Since function(x){return f(x)} === f then you can simplify:

return arrayOfSheeps.filter(Boolean).length;

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