why arrow function return undefined

Question

I'm writing a function that simply loops through a Json schema. Let us say we have a simple json schema such as:

    var foo = {
  "description": "A car  schema",
  "type": "object",
  "properties": {
    "_id": {
      "type": "string"
    },
    "_rev": {
      "type": "string"
    },
    "sources": {
      "type": "object",
      "properties": {
        "mam": {
          "type": "object",
          "properties": {
            "source_id": {
              "type": [ "integer", "null" ]
            },
            "SOR": {
              "type": ["boolean","null"]
            }
          }
        },
        "sas": {
          "type": "object",
          "properties": {
            "source_id": {
              "type": "string"
            },
            "SOR": {
              "type": ["boolean","null"]
            },
            "CAR": {
              "type": ["object","null"]
            }
          }
        }
      }
    }
  }
}

We're trying to collect the type of the key object from it. Here is function search for CAR type should return => "object"

parseObjectProperties = (obj)=> {
  for (var k in obj) {
    if(k === "CAR"){
     console.log(_.values(obj[k])[0][0]) // When I do a console log like this prin the object value
     return  _.values(obj[k])[0][0] // but in return i get undefined 
      }
    if ( _.isObject( obj[k]) && !_.isNil(obj[k])) {
    return  parseObjectProperties(obj[k])
    } 
  }
}


parseObjectProperties(foo);

When I run it, the inner console.log(_.values(obj[k])[0][0]) shows the correct value: object

but if i run it

console.log(parseObjectProperties(foo));

I get

undefined

Why isn't the function properly returning the correct value => "object"?

Thank you!

This is a classic recursion mistake, forgetting to `return` the recursive call. You want `return parseObjectProperties(obj[k])` — Phil, Jun 09 '20 at 01:39
i add the return ```return parseObjectProperties(obj[k]) ``` but still the same error. — Mohamed Eshaftri, Jun 09 '20 at 08:33
Please [update the code in your question](https://stackoverflow.com/posts/62273645/edit) to match what you currently have. — Phil, Jun 09 '20 at 08:37
here is the updated code after add return to the ```return parseObjectProperties(obj[k]) . — Mohamed Eshaftri, Jun 09 '20 at 10:37

Brian Patterson · Accepted Answer · 2020-06-10T06:25:17.697

I just re-wrote this as I didn't understand the logic you were using. Does this solve your problem?

FYI your object CAR, has a property named type whose value is an array that contains 2 values, "object" and "null" so you want to use obj[k].type[0] if you want to get "object" as the result.

const parseObjectProperties = (obj) => {
  var result = null;
  for (var k in obj)
    if (k == "CAR") return obj[k].type[0];
    else if (obj[k] instanceof Object) 
      result = parseObjectProperties(obj[k]);
  return result;
}


var foo = {
  "description": "A car  schema",
  "type": "object",
  "properties": {
    "_id": {
      "type": "string"
    },
    "_rev": {
      "type": "string"
    },
    "sources": {
      "type": "object",
      "properties": {
        "mam": {
          "type": "object",
          "properties": {
            "source_id": {
              "type": ["integer", "null"]
            },
            "SOR": {
              "type": ["boolean", "null"]
            }
          }
        },
        "sas": {
          "type": "object",
          "properties": {
            "source_id": {
              "type": "string"
            },
            "SOR": {
              "type": ["boolean", "null"]
            },
            "CAR": {
              "type": ["object", "null"]
            }
          }
        }
      }
    }
  }
}

console.log(parseObjectProperties(foo));

@MohamedEshaftri Awesome, glad to help! Can you please accept my answer by clicking the checkmark on the left? Thanks! https://stackoverflow.com/help/someone-answers — Brian Patterson, Jun 10 '20 at 04:49

why arrow function return undefined

1 Answers1