eslint: no-case-declaration - case 块中意外的词法声明 [英] eslint: no-case-declaration - unexpected lexical declaration in case block

问题描述

在reducer 中的这种上下文中更新状态的更好方法是什么?

What is the better way to update state in this context inside a reducer?

case DELETE_INTEREST:
    let deleteInterests = state.user.interests;
    let index = deleteInterests.findIndex(i => i == action.payload);
    deleteInterests.splice(index, 1);
    return { ...state, user: { ...state.user, interests: deleteInterests } };

ESLint 不喜欢 reducer 中 case 块内的 let 语句，得到:

ESLint doesn't like let statements inside case blocks inside a reducer, getting:

eslint: no-case-declaration - 意外的词法声明以防万一块

eslint: no-case-declaration - unexpected lexical declaration in case block

推荐答案

ESLint 不喜欢在 case 块内的 let 语句减速机，为什么?

ESLint doesn't like let statements inside case blocks inside a reducer, Why?

不鼓励这样做，因为它会导致变量在当前case 之外的范围内.通过使用块，您可以将变量的范围限制为该块.

This is discouraged because it results in the variable being in scope outside of your current case. By using a block you limit the scope of the variable to that block.

使用 {} 创建带大小写的块作用域，如下所示:

Use {} to create the block scope with case, like this:

case DELETE_INTEREST: {
    let .....
    return (...)
}

检查这个片段:

function withOutBraces() { 
  switch(1){
    case 1: 
      let a=10; 
      console.log('case 1', a); 
    case 2: 
      console.log('case 2', a)
  } 
}

function withBraces() { 
  switch(1){
    case 1: {
      let a=10; 
      console.log('case 1', a); 
    }
    case 2: {
      console.log('case 2', a)
    }
  } 
}

console.log('========First Case ============')
withOutBraces()
console.log('========Second Case ============')
withBraces();

要从数组中删除元素，请使用 array.filter，因为 splice 将对原始数组进行更改.像这样写:

For deleting the element from array, use array.filter, because splice will do the changes in original array. Write it like this:

case DELETE_INTEREST:
    let deleteInterests = state.user.interests;
    let newData = deleteInterests.filter(i => i !== action.payload);
    return { ...state, user: { ...state.user, interests: newData } };

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