JavaScript if(x) vs if(x==true)
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/23061921/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
JavaScript if(x) vs if(x==true)
提问by TheZver
In JavaScript , in which cases the following statements won't be logically equal ?
在 JavaScript 中，在哪些情况下以下语句在逻辑上不相等？
if(x){}
and
和
if(x==true){}
Thanks
谢谢
回答by thefourtheye
They are not at all equal.
他们根本不是平等的。
if (x)
checks if xis Truthy where as the later checks if the Boolean value of xis true.
检查是否x为Truthy，后者检查布尔值是否x为true。
For example,
例如，
var x = {};
if (x) {
console.log("Truthy");
}
if (x == true) {
console.log("Equal to true");
}
Not only an object, any string (except an empty string), any number (except 0(because 0is Falsy) and 1) will be considered as Truthy, but they will not be equal to true.
不仅是一个对象，任何字符串（空字符串除外）、任何数字（除了0（因为0是 Falsy）和1）都将被视为Truthy，但它们不会等于true。
As per ECMA 5.1 Standards, in if (x), Truthiness of xwill be decided, as per the following table
根据ECMA 5.1 标准，在if (x)，真实性x将被确定，如下表
+-----------------------------------------------------------------------+
| Argument Type | Result |
|:--------------|------------------------------------------------------:|
| Undefined | false |
|---------------|-------------------------------------------------------|
| Null | false |
|---------------|-------------------------------------------------------|
| Boolean | The result equals the input argument (no conversion). |
|---------------|-------------------------------------------------------|
| Number | The result is false if the argument is +0, ?0, or NaN;|
| | otherwise the result is true. |
|---------------|-------------------------------------------------------|
| String | The result is false if the argument is the empty |
| | String (its length is zero); otherwise the result is |
| | true. |
|---------------|-------------------------------------------------------|
| Object | true |
+-----------------------------------------------------------------------+
Note:The last line object, which includes both objects and Arrays.
注意：最后一行object，包括对象和数组。
But in the later case, as per The Abstract Equality Comparison Algorithm,
但在后一种情况下，根据抽象平等比较算法，
If Type(x) is Boolean, return the result of the comparison ToNumber(x) == y.
If Type(y) is Boolean, return the result of the comparison x == ToNumber(y).
value of xwill be converted to a number and that number will be checked against true.
的值x将被转换为一个数字，该数字将根据 进行检查true。
Note:
笔记：
In JavaScript, trueis 1and falseis 0.
在 JavaScript 中，trueis1和falseis 0。
console.log(1 == true);
# true
console.log(0 == false);
# true
回答by Darius
Several cases evaluate to false in the first form, such as empty string, 0, undefined, null.
有几种情况在第一种形式中评估为 false，例如空字符串、0、未定义、空值。
If you want to be a bit more semantic about it, try the bang bang in front of the expression:
如果你想对它有更多的语义，试试在表达式前面的 bang bang：
if(!!x){...}
this will convert the expression result to a truthy representing the same semantically. This is closer to an analogue to the expression you describe (x == true)
这会将表达式结果转换为在语义上表示相同的真实值。这更接近于您描述的表达方式的类比(x == true)
Also be aware that ==is value comparions with type coercion, eg "3" == 3, whereas ===asserts equal typing too.
还要注意，这==是与类型强制的值比较，例如"3" == 3，而===断言也等于类型。
So they are not the same, but often logically represent the same test, thanks to the semantics of the language and the !! you can use
因此，由于语言的语义和 !! 您可以使用
