解析xml DTD文件(Parser for xml DTD file)

 var methodsArray=[[{mark:Number,content:String}]]; 这除了methodsArray[0][0]没有任何内容。 
 
 methodsArray[i][x] （或者甚至methodsArray[i] ）是undefined （除了当i===0和x===0 [除了数组方法，例如，再次例如i===0和x==="push"但这是离题）]。 
 
 如您的测试输出中所示，您的循环访问的内容不是methodsArray[0][0]并尝试设置属性。 
 
 如果你想要，你可以在旅途中创建元素： 
 
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
        });
    }
}
 
 在创建methodsArray时，只需要完成一次。 
 
 作为另一个说明，我意识到你可能正在编写Typescript（或者Flow？）。 类型注释不使用=但是:所以它需要是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Array，一个Array又有一个元素是一个对象，其中属性mark是Number构造函数， content是String构造函数。 

var methodsArray=[[{mark:Number,content:String}]]; this does not have anything except methodsArray[0][0].
 
methodsArray[i][x] (or even methodsArray[i]) is undefined (except when i===0 and x===0 [except again for Array methods, e.g. i===0 and x==="push" but that's off the point]).
 
As shown in your test output, your loop is accessing something other than methodsArray[0][0] and trying to set a property.
 
If you want you can create the elements on the go:
 
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
        });
    }
}
 
This is only to be done once though, when creating methodsArray.
 
As another note, i realized you are likely writing Typescript (or maybe Flow?). Type annotations do not use = but :, so it would need to be var methodsArray:{mark:Number,content:String}[][]; or var methodsArray:Array<Array<{ mark:number, content:string }>>;. In Javascript, var methodsArray=[[{ mark:number, content:string }]]; is an Array with one element, an Array with again one element which is an object, where the property mark is the Number constructor and content is the String constructor.