打字稿未定义强迫

我正在写一个终极版减速时，我发现这个代码：打字稿未定义强迫

export function users(state: { myself: IUser | undefined, users: IUser[] } = { myself: undefined, users: [] }, action: UserActions) { 
    const mself = state.myself; 
    if (action.type === EMyselfAction.CHANGE_MYSELF_CONFIG && state.myself !== undefined) { 
    return { 
     myself: myself(mself, action), 
     users: state.users.map((u) => user(u, action, state.myself.id)), 
    }; 
    } 
    ... 
}

是输出错误对象可能是“未定义”：

怎么能state.myself未定义，如果它已被检查，它不是？

来源

2017-08-26 lilezek

的可能的复制【如何抑制打字稿？“错误TS2533：对象可能是‘空’或‘未定义’”]（https://stackoverflow.com/questions/40349987/如何禁止打字脚本错误ts2533对象是可能null或undefine） – k0pernikus

您能否请将错误消息作为文本发布，而不是只发布它作为截图？这可能会帮助其他人面临同样的错误通过谷歌找到问题。 – k0pernikus

由于断言（'T is' type guard或'！== null'检查），TS不会总是“改变”参数的类型。你可能有更好的运气用'mself'替换'state.myself'并声明反对（局部变量更容易改变）。 – ssube

我认为这是因为state.myself是在不同的范围。

export function users(state: { myself: IUser | undefined, users: IUser[] } = { myself: undefined, users: [] }, action: UserActions) { 
    const mself = state.myself; 
    if (action.type === EMyselfAction.CHANGE_MYSELF_CONFIG && state.myself !== undefined) { 
    state.myself // (property) myself: IUser 

    const foo =() => { 
     state.myself // but here is (property) myself: IUser | undefined 
    } 
    // ... 
    } 
    ... 
}

我不认为你可以以其它方式保证，因为你可以使用它在其他地方（不仅在该分支那里state.myself !== undefined）。所以，你可以这样做：

export function users(state: { myself: IUser | undefined, users: IUser[] } = { myself: undefined, users: [] }, action: UserActions) { 
    const mself = state.myself; 
    if (action.type === EMyselfAction.CHANGE_MYSELF_CONFIG && state.myself !== undefined) { 
    const id = state.myself.id; 
    return { 
     myself: myself(mself, action), 
     users: state.users.map((u) => user(u, action, id)), 
    }; 
    } 
    ... 
}

来源

2017-08-26 13:58:04 Federkun

打字稿未定义强迫

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