How make query in JSON with variable substitution

I have JSON file like this (example):

{
"deecracks": [
{
"layercodename": "osm",
"layername": "Open Street Map",
},
{
"layercodename": "olen",
"layername": "tracks",
}
],
      
"theboomtownrats": [
{
"layercodename": "kuku",
"layername": "Open Street Map",
},
{
"layercodename": "olen",
"pathto": "rerere.json",
}
]
}

I can get value what me need:

var megatest = data.theboomtownrats[0].layercodename;

This will be kuku

But theboomtownrats or deecracks or other value like this contain in variable.
If i in code write just data.theboomtownrats[0].layercodename all is work, but if i do like this:

var testmega = `'data.' + ${artist} + '[0].layercodename'`

or just use concatenation text and variable i get just same string in var testmega.

Its possible - substitution value of variable in query? If possible - how?

p.s. I found - this can make over the eval() and this work, but people say it's not safe, and must do over the function, but i have failute with this.

Evaluate an Equation in Javascript, without eval()

You can use bracket notation with javascript objects and pass a variable to them.

So instead of separating with a period, just wrap the string in brackets. And you can pass a variable in the brackets.

let artist = "deecracks";
console.log(data[artist][0]["layercodename"])

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

let data = {
  "deecracks": [{
      "layercodename": "osm",
      "layername": "Open Street Map",
    },
    {
      "layercodename": "olen",
      "layername": "tracks",
    }
  ],

  "theboomtownrats": [{
      "layercodename": "kuku",
      "layername": "Open Street Map",
    },
    {
      "layercodename": "olen",
      "pathto": "rerere.json",
    }
  ]
}

let artist = "deecracks";
console.log(data[artist][0]["layercodename"])

<!-- end snippet -->

Try the bracket notation. Like this:

var artist = 'theboomtownrats';
var megatest = data[artist][0].layercodename;