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 tcs with unique names. Furthermore one tc can have multiple bcs, and bc has a name attribute.

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

what do you mean by better object structure? it depends on the purpose. — Nina Scholz
– Nina Scholz, Commented Apr 21, 2016 at 8:53

Nina Scholz · Accepted Answer · 2016-04-21 09:24:27Z

4

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>');

edited Apr 21, 2016 at 9:24

answered Apr 21, 2016 at 8:30

Nina Scholz

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2 Comments

s1n7ax Over a year ago

I'm sorry i edited the question. i want to add two bcs to tc one. Could you please edit the answer

s1n7ax Over a year ago

It's working but hard to understand function add(o, v). Could you please simplify that if it's possible.

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