How make query in JSON with variable substitution

Question

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()

https://youmightnotneed.com/lodash#get looking for somethig like this? — cmgchess, Apr 06 '23 at 15:32
You can [use bracket notation](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Property_accessors), and pass in the variable name: `data[artist][0].layercodename` — Andy, Apr 06 '23 at 15:33
You can enumerate the keys of an object with Object.keys. In your code, `Object.keys(data)` would equal `[“deecracks”, “theboomtownrats”]` — James, Apr 06 '23 at 15:43
Can you please format your question better? Both code and text are hard to read. Take a look at some highly rated JS questions for examples. — Dommondke, Apr 06 '23 at 16:10

score 1 · Accepted Answer · answered Apr 06 '23 at 15:31

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"])

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"])

Sazedul Haque · Answer 2 · 2023-04-06T16:07:07.550

1

Try the bracket notation. Like this:

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

edited Apr 06 '23 at 16:07

answered Apr 06 '23 at 15:39

Sazedul Haque

21
3

**theboomtownrats** would cause an error as its being passed as a variable and not string – imvain2 Apr 06 '23 at 15:52
Thanks. The answer has been updated. – Sazedul Haque Apr 06 '23 at 16:09
Thank you, this was very simple, i guessed. – issik kul Apr 06 '23 at 16:22

How make query in JSON with variable substitution

2 Answers2