javascript .filter() true 布尔值
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javascript .filter() true booleans
提问by jyoon006
function bouncer(arr) {
// Don't show a false ID to this bouncer.
function a(b) {
if(b !== false) {
return b;
}
}
arr = arr.filter(a);
return arr;
}
bouncer([7, 'ate', '', false, 9]);
I have to return true boolean statements only, and when I run this code, it works. However, I am quite confused because my "if statement" will work whether it's b !== true or b !== false. Could someone please explain the reason why this works both ways?
我只需要返回真正的布尔语句，当我运行这段代码时，它就可以工作了。但是，我很困惑，因为无论是 b !== true 还是 b !== false，我的“if 语句”都有效。有人可以解释为什么这两种方式都有效吗？
回答by hello world
I was solving a similar problem and came up with this:
我正在解决一个类似的问题，并想出了这个：
function bouncer(arr) {
return arr.filter(Boolean);
}
bouncer([7, 'ate', '', false, 9]);
// returns ['7','ate','9']
回答by leonel.ai
Apparently .filter()was introduced in ES5.
显然.filter()是在 ES5 中引入的。
This definitely helped me wrap my mind around what's going on here. Hope it helps!
这绝对帮助我了解这里发生的事情。希望能帮助到你！
Essentially, writing:
本质上，写作：
arr.filter(Boolean)
is the same as writing:
和写一样：
arr.filter( function(x) { return Boolean(x); });
since Boolean()is also a function that returns truthy when true and falsy when false!
因为Boolean()也是一个函数，它在真时返回真，假时返回假！
Example:
例子：
var a = [1, 2, "b", 0, {}, "", NaN, 3, undefined, null, 5];
var b = a.filter(Boolean); // [1, 2, "b", {}, 3, 5];
Source: here.
来源：这里。
回答by mahig
simplest way to do it :
最简单的方法：
function bouncer(arr) {
return arr.filter(x => !!x);
}
回答by Emil Ingerslev
It's because you return the value. The filter function should return true or false like this:
这是因为您返回了值。过滤器函数应该像这样返回真或假：
function bouncer(arr) {
arr = arr.filter(function(x) { console.log(x === true)
if(x !== false) {
return true;
}
});
return arr;
}
or shorter:
或更短：
function bouncer(arr) {
return arr.filter(function(x) { console.log(x === true)
return x !== false;
});
}
回答by jdphenix
Your function acts is it does because JavaScript values in boolean comparisons are "truthy" or "falsey". Non-booleans are coerced to a boolean value when used in a boolean context (comparisons, if statements, etc.)
您的函数会起作用，因为布尔比较中的 JavaScript 值是“真”或“假”。在布尔上下文（比较、if 语句等）中使用时，非布尔值被强制为布尔值
If I understand your intent, you can modify your function to get your expected output like this:
如果我理解您的意图，您可以修改您的函数以获得您的预期输出，如下所示：
function bouncer(arr) {
// Don't show a false ID to this bouncer.
function a(b) {
if(typeof(b) === 'boolean' && !b) {
return new Boolean(b);
}
}
arr = arr.filter(a);
return arr;
}
bouncer([7, 'ate', '', false, 9, true]);
回答by Dr Gaud
I came across this exercise and was playing about with it somewhat. It ended up helping me understand it a bit better, so if you may I will add a bit of clarity to this bouncer function.
我遇到了这个练习，并在某种程度上玩弄它。它最终帮助我更好地理解了它，所以如果你可以的话，我会为这个保镖功能添加一些清晰度。
function bouncerOne(array){
let truthy = array.filter(x => x);
// This takes the .filter() and applies the anon function where it takes
// the value and returns the positive value. All values that are not Falsy including
// objects and functions would return True.
console.log("The Truth is:", truthy);//this Outputs the result to the console.
let falsy = array.filter(x => !x);
//This takes the .filer() and applies the
//annon function where it takes the value and only returns items that ARE NOT True.
//So Falsy Values are taken.
console.log("The Falsy Values are",falsy);
//The annon function of (x => x) & (x => !x)
// really makes use of the strict equality power of JavaScript.
// Where simple conditional test can be carried out.
};
console.log(bouncerOne([7, "ate", "", false, 9,null,42,"Bingo",undefined,NaN]));
//Returns: The Truth is: [ 7, 'ate', 9, 42, 'Bingo' ]
//The Falsy Values are [ '', false, null, undefined, NaN ]
