Building complex JSON in Javascript

Question

Just started using JavaScript and need some guidance on how best to create /build the JSON below on the fly/dynamically.

Some of the keys will need to be from variables. For example in the JSON below, keys called 'variable_key_*' will need to be from a variable.

{
  "static_key_1": "value",
  "static_key_2": [{
    "static_key_3": {
      "id": "1097274153"
    },
    "static_key_4": "value",
    "static_key_5": {
      "static_key_6": {
        "variable_key_1": "value",
        "variable_key_2": "value",
        "variable_key_3": "value"
      },
      "static_key_7": {
        "static_key_8": [
          "value"
        ]
      }
    }
  }]
}

Your question isn't clear, and isn't specific enough. Please edit to rectify that. — isherwood
– isherwood, Commented Feb 14, 2017 at 21:06
your JS object is malformed, the value you affect to "static_key_2" is a mix of an object and an array. First verify your object with a tool like jsonlint.com and then edit your post (the tool works because in your case, the JS object will be directly mapped to a JSON object) :) — ValLeNain
– ValLeNain, Commented Feb 14, 2017 at 21:09
@valLeNain I've checked in JSONLint and fixed errors and reposted. — user45097
– user45097, Commented Feb 14, 2017 at 21:22

Tim Consolazio · Accepted Answer · 2017-02-14 21:39:56Z

2

You can set keys in an object with variables by using bracket notation.

let theVariable = 'useful_name';
let theValue = 12345;
let myObj = {};

myObj [ theVariable ] = theValue;

Will result in:

{ useful_name : 12345 }

And stringify as you'd expect.

Edit based on request for more info:

Say you wanted to create a nested object with an array of objects, we'll use the object we already have.

myObj [ someOtherVar ] = {};
let myObjSomeOtherVar = myObj [ someOtherVar ];
myObjSomeOtherVar [ someOtherKey ] = [ ].push ( { } );
let theArrayOfObjects = myObjSomeOtherVar [ someOtherKey ];
theArrayOfObjects [ 0 ] [ anotherKeyName ] = 'hello';

This would result in (provided you actually declared all the vars etc)

{ useful_name : 12345,
  valOfSomeOtherVar : 
      { valOfSomeOtherKey : 
          [ { valOfAnotherKeyName : 'hello' } ] 
      }
}

The trick is to just develop your data schema abstractly (so the skeleton you want), then write a routine that builds it. I rarely build an object by hand this way unless it's just a small util obj, I usually feed an empty object into a routine to build it out (using loops, recursion, conditionals, whatever). And as for practice, it is always a good idea to have a skeleton at least documented for a data structure, which can also be used as reference to write the function that can generate the whole thing just by passing it some variables for keynames and values. You would write a test for that function that would give you back the objects you'd predict, etc.

edited Feb 14, 2017 at 21:39

answered Feb 14, 2017 at 21:20

Tim Consolazio

4,8882 gold badges21 silver badges29 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

user45097 Over a year ago

Hi @Tim Consolazio, thanks for the feedback. I understand your post. But how would I go about creating the nested parts of the JSON? Say from static_key_2 onwards?

Tim Consolazio Over a year ago

I'd probably write a routine that lets me feed in the info and generates the entire object. I'll post a little sample that shows how to create a single nested array.

user45097 Over a year ago

Hi @Tim Consolazio, just giving this a go now. I've copied and declared vars (changed let to vars as node was complaining) and getting this error: TypeError: Cannot set property 'anotherKeyName' of undefined - theArrayOfObjects [ 0 ] [ anotherKeyName ] = 'hello';.

Tim Consolazio Over a year ago

Did you make sure to push an object onto the array? I'd wager there's no object at theArray [ 0 ]

user45097 Over a year ago

Thanks for the guidance!

ValLeNain · Accepted Answer · 2017-02-14 21:29:54Z

1

If you don't need to create it in one statement (and there is few chance you do), you'd do as follow:

var yourObject = {
  "static_key_1": "value",
  "static_key_2": [{
    "static_key_3": {
        "id": "1097274153"
    },
    "static_key_4": "value",
    "static_key_5": {
        "static_key_6": {},
        "static_key_7": {
            "static_key_8": [
                "value"
            ]
         }
     }
  }]
}

/* Get their value from wherever you want */
var variable_key_1 = 'something';
var variable_key_2 = 'something_else';
var variable_key_3 = 'another_one';

yourObject.static_key_2[0].static_key_5.static_key_6[variable_key_1] = 'value';
yourObject.static_key_2[0].static_key_5.static_key_6[variable_key_2] = 'value';
yourObject.static_key_2[0].static_key_5.static_key_6[variable_key_3] = 'value';

The strategy is to build the objects with properties with variables names after the ones with static names, using the brackets notation.

This will result in:

{
  "static_key_1": "value",
  "static_key_2": [{
    "static_key_3": {
        "id": "1097274153"
    },
    "static_key_4": "value",
    "static_key_5": {
        "static_key_6": {
          "something": "value",
          "something_else": "value",
          "another_one": "value"
        },
        "static_key_7": {
            "static_key_8": [
                "value"
            ]
         }
     }
  }]
}

answered Feb 14, 2017 at 21:29

ValLeNain

2,3542 gold badges23 silver badges40 bronze badges

2 Comments

user45097 Over a year ago

Hi @vallenain, Thanks for the feedback. I've run the above via Node cmd line. When I console.out(yourObject) sometthing isn't right as it only shows the following

{ static_key_1: 'value',   static_key_2:     [ { static_key_3: [Object],        static_key_4: 'value',        static_key_5: [Object] } ] }

ValLeNain Over a year ago

that's just the way it's printed. The object itself should be as expected.

Collectives™ on Stack Overflow

Building complex JSON in Javascript

2 Answers 2

5 Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

5 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related