How to append arrays to existing json array and write to file in node js

Question

I have a example.json file.

{
  "tc" :
  [
    {"name" : "tc_001"},
    {"name" : "tc_002"},
    {"name" : "tc_003"},
    {"name" : "tc_004"},
    {"name" : "tc_005"}
  ]
}

In here I need to add another array to the tc[0]th index. In Node JS I tried this:

var fs = require('fs');

var obj = JSON.parse(fs.readFileSync('example.json', 'utf8'));
var arr1 = {bc :[{name:'bc_001'}]}
var arr2 = {bc :[{name:'bc_002'}]}
obj.tc[0] = arr1;
obj.tc[0] = arr2;

But when printing that obj , obj.tc[0] has replaced by value of arr2 . The final result I want to achieve is:

{
  "tc" :
  [
    {
       "name" : "tc_001"
       "bc" :
       [
            {"name" = "bc_001"},
            {"name" = "bc_002"}
       ]
    },
    {"name" : "tc_002"},
    {"name" : "tc_003"},
    {"name" : "tc_004"},
    {"name" : "tc_005"}
  ]
}

I also want to write this back to the same json file. I'm trying to achieve here a file containing number of tc s with unique names. Furthermore one tc can have multiple bc s, and bc has a name attribute.

I also accept suggestion on a better json structure to support this concept.

Answer 1

A solution for more than one item to add to the object.

It uses an object o where the new values should go and a value object v with the keys and the items to assign.

Inside it iterates over the keys and build a new array if not already there. Then all values are pushed to the array.

 function add(o, v) { Object.keys(v).forEach(k => { o[k] = o[k] || []; v[k].forEach(a => o[k].push(a)); }); } var obj = { "tc": [{ "name": "tc_001" }, { "name": "tc_002" }, { "name": "tc_003" }, { "name": "tc_004" }, { "name": "tc_005" }] }; add(obj.tc[0], { bc: [{ name: 'bc_001' }] }); add(obj.tc[0], { bc: [{ name: 'bc_002' }] }); document.write('<pre>' + JSON.stringify(obj, 0, 4) + '</pre>');