How to parse this JSON on Javascript

Question

I have this JSON from Mongoose error catching on a NodeJS app with the express framework:

{
  "err": {
    "errors": {
      "last_name": {
        "message": "Path `last_name` is required.",
        "name": "ValidatorError",
        "properties": {
          "message": "Path `last_name` is required.",
          "type": "required",
          "path": "last_name"
        },
        "kind": "required",
        "path": "last_name"
      },
      "first_name": {
        "message": "Path `first_name` is required.",
        "name": "ValidatorError",
        "properties": {
          "message": "Path `first_name` is required.",
          "type": "required",
          "path": "first_name"
        },
        "kind": "required",
        "path": "first_name"
      },
      "password": {
        "message": "Path `password` (`iam`) is shorter than the minimum allowed length (6).",
        "name": "ValidatorError",
        "properties": {
          "message": "Path `password` (`iam`) is shorter than the minimum allowed length (6).",
          "type": "minlength",
          "minlength": 6,
          "path": "password",
          "value": "iam"
        },
        "kind": "minlength",
        "path": "password",
        "value": "iam"
      }
    },
    "_message": "User validation failed",
    "message": "User validation failed: last_name: Path `last_name` is required., first_name: Path `first_name` is required., password: Path `password` (`iam`) is shorter than the minimum allowed length (6).",
    "name": "ValidationError"
  }
}

How can I get the type and path of each error inside the properties, I have tried forEach() method but it didn't work, is there any other way to loop through this JSON?

Possible duplicate of [How do I loop through or enumerate a JavaScript object?](https://stackoverflow.com/questions/684672/how-do-i-loop-through-or-enumerate-a-javascript-object) — kgrg, May 19 '19 at 19:38

Randy Casburn · Accepted Answer · 2019-05-19T18:38:20.903

Find the keys, the iterate over the keys. Add those results to some data structure.

I've chose to use map on the keys and added to an array.

const errors = {
      "err": {
        "errors": {
          "last_name": {
            "message": "Path `last_name` is required.",
            "name": "ValidatorError",
            "properties": {
              "message": "Path `last_name` is required.",
              "type": "required",
              "path": "last_name"
            },
            "kind": "required",
            "path": "last_name"
          },
          "first_name": {
            "message": "Path `first_name` is required.",
            "name": "ValidatorError",
            "properties": {
              "message": "Path `first_name` is required.",
              "type": "required",
              "path": "first_name"
            },
            "kind": "required",
            "path": "first_name"
          },
          "password": {
            "message": "Path `password` (`iam`) is shorter than the minimum allowed length (6).",
            "name": "ValidatorError",
            "properties": {
              "message": "Path `password` (`iam`) is shorter than the minimum allowed length (6).",
              "type": "minlength",
              "minlength": 6,
              "path": "password",
              "value": "iam"
            },
            "kind": "minlength",
            "path": "password",
            "value": "iam"
          }
        },
        "_message": "User validation failed",
        "message": "User validation failed: last_name: Path `last_name` is required., first_name: Path `first_name` is required., password: Path `password` (`iam`) is shorter than the minimum allowed length (6).",
        "name": "ValidationError"
      }
    }
 let output = Object.keys(errors.err.errors).map(key => { return {type:errors.err.errors[key].properties.type, path:errors.err.errors[key].properties.path} });
 console.log(output);

`map` returns an array. You do not need to first create `output =[]` and then pushing in the function. Just do `let output=Object.keys(errors.err.errors).map(key =>({type:errors.err.errors[key].properties.type, path:errors.err.errors[key].properties.path}))`. If you don't want the array, use `forEach` instead to iterate over the array. — some, May 19 '19 at 18:36
You don't need to use `return` in the arrow-function, but since you are returning an object you must enclose it in parentheses (or it will be interpreted as a statement). `key => ({type:"error"})` works, `key => {type:"error"}` doesn't, `key => {return {type:"error"}}` works but is longer to type.. — some, May 19 '19 at 18:44

score 1 · Answer 2 · edited Jun 20 '20 at 09:12

1

Another alternative is to use for ... in to traverse the object properties of err.errors:

Example:

const input = {"err":{"errors":{"last_name":{"message":"Path `last_name` is required.","name":"ValidatorError","properties":{"message":"Path `last_name` is required.","type":"required","path":"last_name"},"kind":"required","path":"last_name"},"first_name":{"message":"Path `first_name` is required.","name":"ValidatorError","properties":{"message":"Path `first_name` is required.","type":"required","path":"first_name"},"kind":"required","path":"first_name"},"password":{"message":"Path `password` (`iam`) is shorter than the minimum allowed length (6).","name":"ValidatorError","properties":{"message":"Path `password` (`iam`) is shorter than the minimum allowed length (6).","type":"minlength","minlength":6,"path":"password","value":"iam"},"kind":"minlength","path":"password","value":"iam"}},"_message":"User validation failed","message":"User validation failed: last_name: Path `last_name` is required., first_name: Path `first_name` is required., password: Path `password` (`iam`) is shorter than the minimum allowed length (6).","name":"ValidationError"}};

for (const k in input.err.errors)
{
    const properties = input.err.errors[k].properties;
    console.log("Error for " + k);
    console.log("> Type: " + properties.type);
    console.log("> Path: " + properties.path);
    console.log("> Message: " + properties.message);
}

.as-console {background-color:black !important; color:lime;}
.as-console-wrapper {max-height:100% !important; top:0;}

edited Jun 20 '20 at 09:12

Community

1
1

answered May 19 '19 at 18:44

Shidersz

16,846
2
23
48

Better to use [for....of](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...of) since for...in also gives you keys in the prototype chain. – some May 19 '19 at 18:48
@some But, to use `for ... of` I will have to do something like `for (k of Object.keys(input.err.errors))` since it won't work directly over the object. And in this case, whit an array of keys, I will prefer to use built-in array methods like shown on the other answer. – Shidersz May 19 '19 at 18:54
Use `for (const [key,value] of Object.entries(input.err.errors))` and instead of making lookups in `input.err.errors[k]` every time, use the variables key or value (or what you called them) – some May 19 '19 at 19:03
@some Ok, it is another alternative, but not what I have tried to show. I just tried to show how to traverse some object directly, not converting first to an array of `keys` or `entries`. – Shidersz May 19 '19 at 19:07
Look at your code. You use `input.err.errors[k]` twice. And you would have used it three times if you also printed the message. Every time you do `input.err.errors[k]` you make a lookup. At least save that as a constant for each iteration. `const value = input.err.errors[k]` instead of making the exact same lookup multiple times. It is not premature optimization. It is less to type, less chance to make a typo, easier to change if the path changes. – some May 19 '19 at 19:12

How to parse this JSON on Javascript

2 Answers2

Example: