使用括号表示法构建一个新的嵌套 object

Question

I'm trying to build a new nested object based on bracked notation. my syntax is

metaObj[subCat][attribute] = value;

and I have these variables; My goal is to achieve this structure

metaObj = {
   chart : {
      x: "random",
      y: 123
   },
   data : {
      x: "random",
      y: 123
   }
}

I should build it dynamically since the attribute names and categories might change in every scenario

I receive this error though

Uncaught TypeError: Cannot set property ---- of undefined

Answer 1

The error says that it cannot set property of undefined because the subCat is undefined.

A solution would be to first define it as an object and then do your thing.

metaObj = {}; 
metaObj[subCat] = {}; // define the subCat ( metaObj: {subCat: {}})
metaObj[subCat][attribute] = value;

Answer 2

That's becoz you are trying to set the value for an object that is not yet created. Assuming that the metaObj is already initialized with {}

if(!metaObj[subCat]) {
 metaObj[subCat]= {};
 metaObj[subCat][attribute] = value;
} else {
 metaObj[subCat][attribute] = value;
}