TypeScript - 是否有一个选项可以禁止在除布尔值之外的任何内容前面使用“！

Question

我知道这可能是一个经典的 javascript 问题，但我发现自己经常使用：

if (!something) {
    //...
}

在 TypeScript 中验证此 something 不是 undefined 或 null。

这很容易出错！在number 上使用时，“0”将匹配，而在enum 上使用时，第一项也将匹配（默认情况下，第一项的值为“0”）！

有没有办法在 TypeScript 中处理这个问题？有没有办法将 TypeScript 配置为禁止在除 boolean（和 any）之外的任何内容前面使用感叹号？这种配置有意义还是我遗漏了一些微不足道的东西？

应该：

if (something === null || something === undefined) {
    //...
}

改为用于验证是否已定义某些内容？有没有办法在团队中强制执行？

Answer 1

您可以使用strict-boolean-expressions TSLint 规则来禁止此类事情。

您可以查看规则here 的一些示例，但这是与您的问题特别相关的摘录。规则会发现错误的地方标有~~~，错误消息写在该标记旁边：

/*** PrefixUnary Expressions ***/
/*** Invalid ***/
!!numType;
  ~~~~~~~  [This type is not allowed in the operand for the '!' operator because it is a number. Only booleans are allowed.]
!strType;
 ~~~~~~~  [This type is not allowed in the operand for the '!' operator because it is a string. Only booleans are allowed.]
!objType;
 ~~~~~~~  [This type is not allowed in the operand for the '!' operator because it is always truthy. Only booleans are allowed.]
!enumType;
 ~~~~~~~~  [This type is not allowed in the operand for the '!' operator because it is an enum. Only booleans are allowed.]
!!classType;
  ~~~~~~~~~  [This type is not allowed in the operand for the '!' operator because it is always truthy. Only booleans are allowed.]
!bwrapType;
 ~~~~~~~~~  [This type is not allowed in the operand for the '!' operator because it is always truthy. Only booleans are allowed.]
!!undefined;
 ~~~~~~~~~~  [This type is not allowed in the operand for the '!' operator because it is always truthy. Only booleans are allowed.]
  ~~~~~~~~~  [This type is not allowed in the operand for the '!' operator because it is always falsy. Only booleans are allowed.]

/*** Valid ***/
!!boolFn();
!boolExpr;
!!boolType;

/*** If Statement ***/
/*** Invalid ***/
if (numType) { /* statements */ }
    ~~~~~~~                       [This type is not allowed in the 'if' condition because it is a number. Only booleans are allowed.]
if (objType) { /* statements */ }
    ~~~~~~~                       [This type is not allowed in the 'if' condition because it is always truthy. Only booleans are allowed.]
if (strType) { /* statements */ }
    ~~~~~~~                       [This type is not allowed in the 'if' condition because it is a string. Only booleans are allowed.]
if (bwrapType) { /* statements */ }
    ~~~~~~~~~                       [This type is not allowed in the 'if' condition because it is always truthy. Only booleans are allowed.]
if (strFn()) { /* statements */ }
    ~~~~~~~                       [This type is not allowed in the 'if' condition because it is a string. Only booleans are allowed.]
if (MyEnum.A) { /* statements */ }
    ~~~~~~~~                       [This type is not allowed in the 'if' condition because it is an enum. Only booleans are allowed.]
if (classType) { /* statements */ }
    ~~~~~~~~~                       [This type is not allowed in the 'if' condition because it is always truthy. Only booleans are allowed.]

---

为了简要回答您的另一面问题，以下代码片段是检查是否已定义某些内容的好方法：

if (something == null) {
    // will enter here if `something === null || something === undefined`
}

有关上述内容的更多详细信息，请参阅here