JSON, node.js: access classes via its name (String)

Question

Here's my situation, I have a JSON that looks somewhat like this:

{
    "items": [{
            "type": "condition",
            "data": {
                "type": "comparison",
                "value1": {
                    "source": "MyType1",
                    "component": "Attribute1"
                },
                "value2": {
                    "source": "MyType2",
                    "component": "Attribute2"
                },
                "operator": "gt"
            }
        },
        {
            "type": "then",
            "data": {
                "result": "failed",
                "message": "value1 is too high"
            }
        }
    ]
}

and would want it to translate to:

if (MyType1.Attribute1 > MyType2.Attribute2) {
    result = "failed";
    console.log("value1 is too high");
}

Now my problem is, I don't know how I would translate the entries of value1 and value2 to actual code, or rather, how I could access the Object MyType1 (maybe through something like getAttribute("MyType1") ). Since I am going to have a whole bunch of sources which each have different components, I cant really write a huge dictionary. Or I would like to avoid it.

The goal is to allow creating if - then - statements via some interactive UI, and I figured it'd be best to save that code as .json files. (Think rule management system).

So, TL,DR, How would I access a Class Attribute this.MyType , if I only have a String MyType to go from? And how would I access the value this.MyType.MyValue , if I get another String MyValue ?

Thanks in advance.

Edit: I'd really like to avoid using eval, for obvious reasons. And if I have to - I guess I would need to create Dictionaries for possible JSON Values, to validate the input?

Answer 1

You need some kind of parser. At first we need some way to store variables and maybe flags:

const variables = {};
var in = false;

Then we go through the code and execute it:

for(const command of items){
  switch( command.type ){
   case "condition":
     //...
   case "then":
    //...
  }
}

To access a variable we can simply do

var current = variables[ identifier ];

To store its the other way round:

variables[ identifier ] = current;