Question

我知道这可能是一个经典的javascript问题，但我经常发现自己使用：

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

在TypeScript中验证此something不是undefined或null。

这非常容易出错！在number上使用时，“0”将匹配，当在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？有没有办法配置TypeScript以禁止除boolean（和any）之外的任何内容的感叹号？这种配置是否有意义，或者我错过了一些微不足道的东西？

应该：

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

是否可以使用

来验证是否定义了某些内容？有没有办法在团队中强制执行此操作？

Answer 1

您可以使用strict-boolean-expressions TSLint规则禁止此类事件。

您可以看到规则here的一些示例，但这是与您的问题特别相关的摘录。规则发现错误的位置标有~~~，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.]

要简要回答您的另一方面的问题，下面的代码剪切是检查某些内容是否定义的好方法：

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

有关上述

的更多详情，请参阅here

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

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