无法将“标记”的属性设置为未定义

Question

这是一个奇怪的错误，因为它看起来是错误的，错误是：

TypeError: Cannot set property 'mark' of undefined
at /home/ubuntu/workspace/tests/app.js:194:36
at Layer.handle [as handle_request](/home/ubuntu/workspace/tests/node_modules/express/lib/router/layer.js:95:5)
at next (/home/ubuntu/workspace/tests/node_modules/express/lib/router/route.js:131:13)
at Route.dispatch (/home/ubuntu/workspace/tests/node_modules/express/lib/router/route.js:112:3)
at Layer.handle [as handle_request] (/home/ubuntu/workspace/tests/node_modules/express/lib/router/layer.js:95:5)
at /home/ubuntu/workspace/tests/node_modules/express/lib/router/index.js:277:22
at Function.process_params (/home/ubuntu/workspace/tests/node_modules/express/lib/router/index.js:330:12)
at next (/home/ubuntu/workspace/tests/node_modules/express/lib/router/index.js:271:10)
at SessionStrategy.module.exports.strategy.pass (/home/ubuntu/workspace/tests/node_modules/passport/lib/middleware/authenticate.js:325:9)
at SessionStrategy.authenticate (/home/ubuntu/workspace/tests/node_modules/passport/lib/strategies/session.js:71:10)
at attempt (/home/ubuntu/workspace/tests/node_modules/passport/lib/middleware/authenticate.js:348:16)
at authenticate (/home/ubuntu/workspace/tests/node_modules/passport/lib/middleware/authenticate.js:349:7)
at Layer.handle [as handle_request] (/home/ubuntu/workspace/tests/node_modules/express/lib/router/layer.js:95:5)
at trim_prefix (/home/ubuntu/workspace/tests/node_modules/express/lib/router/index.js:312:13)
at /home/ubuntu/workspace/tests/node_modules/express/lib/router/index.js:280:7
at Function.process_params (/home/ubuntu/workspace/tests/node_modules/express/lib/router/index.js:330:12)

产生这个错误的代码是：

for(var i = 0;i < req.body.numOfMethods;i++)
{
    for(var x = 0;x< numOfParts[i];x++)
    {
        methodsArray[i][x].mark=parts[i][x].mark;
        methodsArray[i][x].content=parts[i][x].content;
    }
}

然而当我在这个文本下运行代码时

console.log("numOfParts[i] = "+numOfParts[0]);
console.log("numOfParts[i] = "+numOfParts[1]);
console.log("numOfMethods = "+req.body.numOfMethods);
for(var i = 0;i < req.body.numOfMethods;i++)
{
    for(var x = 0;x< numOfParts[i];x++)
    {
        console.log("i = "+i);
        console.log("x = "+x);
        console.log("parts[i][x].mark = "+parts[i][x].mark);
        console.log("parts[i][x].content = "+parts[i][x].content);
    }
}

打印出来：

numOfParts[i] = 3
numOfParts[i] = 2
numOfMethods = 2
i = 0
x = 0
parts[i][x].mark = 2
parts[i][x].content = test
i = 0
x = 1
parts[i][x].mark = 2
parts[i][x].content = test
i = 0
x = 2
parts[i][x].mark = 2
parts[i][x].content = test
i = 1
x = 0
parts[i][x].mark = 3
parts[i][x].content = test
i = 1
x = 1
parts[i][x].mark = 3
parts[i][x].content = test

这非常表明methodsArray[i][x].mark 没有被设置为未定义的值。所以最终在这里我很迷茫我应该怎么做才能修复这个错误。

这里是我定义有问题的数组的地方（如果我的错误存在于这段代码中）

var methodsArray=[[{mark:Number,content:String}]];
    var numOfParts=[req.body.m1parts,req.body.m2parts,req.body.m3parts,req.body.m4parts];
    var parts=[
        [
            {mark:req.body.m1p1mark,content:req.body.m1p1content},{mark:req.body.m1p2mark,content:req.body.m1p2content},
            {mark:req.body.m1p3mark,content:req.body.m1p3content},{mark:req.body.m1p4mark,content:req.body.m1p4content},
            {mark:req.body.m1p5mark,content:req.body.m1p5content},{mark:req.body.m1p6mark,content:req.body.m1p6content},
            {mark:req.body.m1p7mark,content:req.body.m1p7content},{mark:req.body.m1p8mark,content:req.body.m1p8content},
            {mark:req.body.m1p9mark,content:req.body.m1p9content},{mark:req.body.m1p10mark,content:req.body.m1p10content}
        ],
        [
            {mark:req.body.m2p1mark,content:req.body.m2p1content},{mark:req.body.m2p2mark,content:req.body.m2p2content},
            {mark:req.body.m2p3mark,content:req.body.m2p3content},{mark:req.body.m2p4mark,content:req.body.m2p4content},
            {mark:req.body.m2p5mark,content:req.body.m2p5content},{mark:req.body.m2p6mark,content:req.body.m2p6content},
            {mark:req.body.m2p7mark,content:req.body.m2p7content},{mark:req.body.m2p8mark,content:req.body.m2p8content},
            {mark:req.body.m2p9mark,content:req.body.m2p9content},{mark:req.body.m2p10mark,content:req.body.m2p10content}
        ],
        [
            {mark:req.body.m3p1mark,content:req.body.m3p1content},{mark:req.body.m3p2mark,content:req.body.m3p2content},
            {mark:req.body.m3p3mark,content:req.body.m3p3content},{mark:req.body.m3p4mark,content:req.body.m3p4content},
            {mark:req.body.m3p5mark,content:req.body.m3p5content},{mark:req.body.m3p6mark,content:req.body.m3p6content},
            {mark:req.body.m3p7mark,content:req.body.m3p7content},{mark:req.body.m3p8mark,content:req.body.m3p8content},
            {mark:req.body.m3p9mark,content:req.body.m3p9content},{mark:req.body.m3p10mark,content:req.body.m3p10content}
        ],
        [
            {mark:req.body.m4p1mark,content:req.body.m4p1content},{mark:req.body.m4p2mark,content:req.body.m4p2content},
            {mark:req.body.m4p3mark,content:req.body.m4p3content},{mark:req.body.m4p4mark,content:req.body.m4p4content},
            {mark:req.body.m4p5mark,content:req.body.m4p5content},{mark:req.body.m4p6mark,content:req.body.m4p6content},
            {mark:req.body.m4p7mark,content:req.body.m4p7content},{mark:req.body.m4p8mark,content:req.body.m4p8content},
            {mark:req.body.m4p9mark,content:req.body.m4p9content},{mark:req.body.m4p10mark,content:req.body.m4p10content}
        ]
    ];

Answer 1

var methodsArray=[[{mark:Number,content:String}]]; 除了methodsArray[0][0] 之外什么都没有。

methodsArray[i][x]（甚至methodsArray[i]）是undefined（i===0 和x===0 除外[数组方法除外，例如i===0 和x==="push"，但这不是重点]）。

如您的测试输出所示，您的循环正在访问 methodsArray[0][0] 以外的其他内容并尝试设置属性。

如果您愿意，您可以随时随地创建元素：

var methodsArray = [];
for(var i = 0; i < req.body.numOfMethods; i++)
{
    methodsArray.push([]);
    for(var x = 0; x< numOfParts[i]; x++)
    {
        methodsArray.push({
          mark: parts[i][x].mark,
          content: parts[i][x].content
        });
    }
}

这只能在创建 methodsArray 时执行一次。

另外，我意识到您可能正在编写 Typescript（或者 Flow？）。类型注释不使用=，而是使用:，因此它需要是var methodsArray:{mark:Number,content:String}[][]; 或var methodsArray:Array<Array<{ mark:number, content:string }>>;。在 Javascript 中，var methodsArray=[[{ mark:number, content:string }]]; 是一个包含一个元素的数组，一个包含一个元素的数组，它是一个对象，其中属性 mark 是 Number 构造函数，content 是 String 构造函数。