Unable to assign the property 'mark' as undefined

Question

Unable to assign the property 'mark' as undefined

The error message is puzzling as it seems to indicate a problem with setting the 'mark' property of undefined:

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)
...

The code snippet causing this error is:

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;
    }
}

However, running the debugging code below produces the following output:

numOfParts[i] = 3
numOfParts[i] = 2
numOfMethods = 2
...

This output confirms that methodsArray[i][x].mark is indeed being assigned values properly. Therefore, the source of the error remains unclear.

Here's where the arrays used in the code are defined:

var methodsArray=[[{mark:Number,content:String}]];
    var numOfParts=[req.body.m1parts,req.body.m2parts,req.body.m3parts,req.body.m4parts];
    ...

javascript arrays mongodb mongoose

Answer 1

Answer №1

var methodsArray=[[{mark:Number,content:String}]];

This specific code snippet focuses solely on methodsArray[0][0].

In cases where methodsArray[i][x] (or methodsArray[i]) is accessed, it typically returns as undefined, unless the values of i and x meet very specific conditions. These exceptions are not within the main scope of discussion.

The issue arises when the loop in your test output attempts to access elements other than methodsArray[0][0] and tries to assign a property.

If necessary, elements can be dynamically created during runtime using the following sample code:

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
        });
    }
}

Note that this process should only occur once during the initial creation of methodsArray.

On a separate note, if you are working with Typescript or Flow, type annotations should use : instead of =. For example, it should be written as

var methodsArray:{mark:Number,content:String}[][];

or

var methodsArray:Array<Array<{ mark:number, content:string }>>;

. In Javascript,

var methodsArray=[[{ mark:number, content:string }]];

represents an array structure containing one element - an array with a single object holding properties mark assigned to the Number constructor and content assigned to the String constructor.

Answer 2

var methodsArray=[[{mark:Number,content:String}]];

This specific code snippet focuses solely on methodsArray[0][0].

In cases where methodsArray[i][x] (or methodsArray[i]) is accessed, it typically returns as undefined, unless the values of i and x meet very specific conditions. These exceptions are not within the main scope of discussion.

The issue arises when the loop in your test output attempts to access elements other than methodsArray[0][0] and tries to assign a property.

If necessary, elements can be dynamically created during runtime using the following sample code:

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
        });
    }
}

Note that this process should only occur once during the initial creation of methodsArray.

On a separate note, if you are working with Typescript or Flow, type annotations should use : instead of =. For example, it should be written as

var methodsArray:{mark:Number,content:String}[][];

or

var methodsArray:Array<Array<{ mark:number, content:string }>>;

. In Javascript,

var methodsArray=[[{ mark:number, content:string }]];

represents an array structure containing one element - an array with a single object holding properties mark assigned to the Number constructor and content assigned to the String constructor.

Unable to assign the property 'mark' as undefined

Answer №1

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