eslint - 代码规范性问题集锦

目录

前言

类型一、Expected '===' and instead saw '=='

类型二、Use '!==' to compare with null

类型三、'*' was used before it was defined

类型四、 '*' is defined but never used

类型五、Unexpected negated condition

类型六、 '*' is not defined

类型七、Unexpected mix of '/' and '-'

类型八、Unexpected string concatenation of literals

类型九、Expected '===' and instead saw '=='

类型十、'*' is already declared in the upper scope

类型十一、This line has a length of *. Maximum allowed is 120

类型十二、Function declared in a loop contains unsafe references to variable(s)

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前言

最近为了规范化代码风格，项目组内启用了VSCode插件eslint，了解eslint的同学都知道，它是在 ECMAScript/JavaScript 代码中识别和报告模式匹配的工具，给出一些代码规范建议，其目的是为了保证代码的一致性和避免一些可能出现的错误。 都有 

类型一、Expected '===' and instead saw '=='

提示警告的波浪线如下图所示： 

报错的意思是应该使用“===”代替“==”，具体警告信息：

{
	"resource": "/g:/project/*/main.js",
	"owner": "eslint",
	"code": {
		"value": "eqeqeq",
		"target": {
			"$mid": 1,
			"external": "https://eslint.org/docs/rules/eqeqeq",
			"path": "/docs/rules/eqeqeq",
			"scheme": "https",
			"authority": "eslint.org"
		}
	},
	"severity": 8,
	"message": "Expected '===' and instead saw '=='.",
	"source": "eslint",
	"startLineNumber": 783,
	"startColumn": 27,
	"endLineNumber": 783,
	"endColumn": 29
}

其中，指明了警告的位置，包括行号，列号，范围等信息。修改后如下图所示，警告波浪线消失：

类型二、Use '!==' to compare with null

提示警告的波浪线如下图所示：  

 警告的意思是应该使用“!==”去和null做判断，修改后如下图所示，警告波浪线消失：

类型三、'*' was used before it was defined

实例：'mainWindow' was used before it was defined.

提示警告的波浪线如下图所示：  

警告的意思是应该某个对象在它正式定义之前就被违规使用了，具体警告信息：

{
	"resource": "/g:/project/*/main.js",
	"owner": "eslint",
	"code": {
		"value": "no-use-before-define",
		"target": {
			"$mid": 1,
			"external": "https://eslint.org/docs/rules/no-use-before-define",
			"path": "/docs/rules/no-use-before-define",
			"scheme": "https",
			"authority": "eslint.org"
		}
	},
	"severity": 8,
	"message": "'mainWindow' was used before it was defined.",
	"source": "eslint",
	"startLineNumber": 204,
	"startColumn": 9,
	"endLineNumber": 204,
	"endColumn": 19
}

解决方法是调整代码顺序，修改后如下图所示，警告的波浪线消失：

类型四、 '*' is defined but never used

 提示警告的波浪线如下图所示：  

 

警告的意思是某些对象被定义了，但是没有被使用到。解决方式是去掉没有必要的声明对象 ，修改后如下图所示，警告的波浪线消失：

类型五、Unexpected negated condition

 提示警告的波浪线如下图所示：  

警告的意思是不正常的判断形式，mPenOpen可以直接作为一个判断条件，而不用多此一举加个“!”非运算符， 修改后如下图所示，警告的波浪线消失：

类型六、 '*' is not defined

 提示警告的波浪线如下图所示：  

警告的意思是某些对象没有定义就被使用了，解决方式是正式声明这些对象， 修改后如下图所示，警告的波浪线消失：

类型七、Unexpected mix of '/' and '-'

 提示警告的波浪线如下图所示：  

警告的意思是不用运算符混合使用了，解决方法是使用小括号明确运算过程的优先级。修改后如下图所示，警告的波浪线消失：

类型八、Unexpected string concatenation of literals

 提示警告的波浪线如下图所示：   

警告的意思是异常的字符串连接方式，修改后如下图所示，警告的波浪线消失：

类型九、Expected '===' and instead saw '=='

 提示警告的波浪线如下图所示：    

警告的意思是建议使用“===”代替“==”，修改后如下图所示，警告的波浪线消失： 

类型十、'*' is already declared in the upper scope

 提示警告的波浪线如下图所示：    

警告的意思是该变量名之前被定义了，此处属于重复定义，修改后如下图所示，警告的波浪线消失：  

类型十一、This line has a length of *. Maximum allowed is 120

 提示警告的波浪线如下图所示：    

警告的意思是某行代码长度超过了最大值限制，具体内容如下所示：

{
	"resource": "/g:/project/*/main.js",
	"owner": "eslint",
	"code": {
		"value": "max-len",
		"target": {
			"$mid": 1,
			"external": "https://eslint.org/docs/rules/max-len",
			"path": "/docs/rules/max-len",
			"scheme": "https",
			"authority": "eslint.org"
		}
	},
	"severity": 8,
	"message": "This line has a length of 402. Maximum allowed is 120.",
	"source": "eslint",
	"startLineNumber": 98,
	"startColumn": 1,
	"endLineNumber": 98,
	"endColumn": 1
}

 解决方式有两种，方法一是明确允许该行代码超出最大长度限制，如下图所示：

方法二是折行处理这段代码，同时使用eslint-disable-next-line no-multi-str声明，具体如下图所示：

类型十二、Function declared in a loop contains unsafe references to variable(s)

警告⚠️：Function declared in a loop contains unsafe references to variable(s) 'count'.

提示警告的波浪线如下图所示： 

解决方式使用eslint-disable-next-line no-loop-func明确声明知道这样的操作行为，修改后如下图所示，警告的波浪线消失：