Searching deeply nested object array for a single key

Question

I am trying to search through a deeply nested array and find if a key exists anywhere inside. I have written up a piece of code which does the traversal, but because it is not recursive (only self calling) it cannot return whether or not it has found anything. It just returns undefined since it reaches the end of the function on one of passes.

I was wondering if there was a way I could do this which would allow me to return true on the first occurrence of a specific key.

Here is a JS bin of what I have been working with so far:

https://jsbin.com/qaxuwajuso/edit?js,console

And here is a direct paste of the code from the above example:

function traverse(item, key) {
    if (typeof item === 'object' && !Array.isArray(item) && item !== null) {
        // Object
        for (let itemKey in item) {
            if (itemKey === key) {
                // Is it possible to return true and break out of the function here?
                console.log('found the key: ' + itemKey + ' With value: ' + item[itemKey]);
            }

            traverse(item[itemKey], key);
        }
    } else if (Array.isArray(item)) {
        // Array
        for (let i = 0; i < item.length; ++i) {
            traverse(item[i], key);
        }
    }
}

Any help would be greatly appreciated. Thank you for your time!

This is nothing like a JSON Array or a JSON Object. JSON is string base representation of data, that has to be parsed using JSON.parse before it can be traversed. What you assign to data is a regular Array. — t.niese
– t.niese, Commented Aug 23, 2018 at 16:45
Updated the title to signify that I am trying to traverse a object array instead of JSON. Thanks! — Chris Frank
– Chris Frank, Commented Aug 23, 2018 at 16:48
Because it has a fall through when the data coming in is not a object or an array. My definition of recursive might be wrong through. — Chris Frank
– Chris Frank, Commented Aug 23, 2018 at 16:49

James · Accepted Answer · 2018-08-23 16:51:15Z

Sure you just need to return a flag of some kind to trigger the loops to stop

/*
 * I am trying to search the following json array for any occurance of the key "statePath".
 * In a perfect world I would be able to find the first occurance, and return true from the
 * function.
 *
 * The following data is not real, I was just trying to write as much nested stuff as possible
 * to test that it traverses as far as needed.
 */

const data = [
    {
        id: '2144d998-4c33-4b03-93d2-f6c675b24508',
        element: 'div',
        props: {
            className: 'testing',
            name: [
                {
                    first: 'John',
                    last: {
                        statePath: 'lastName',
                        anArray: [
                          {
                            anObject: {
                              anotherArray: [
                                {
                                  doesItWork: {
                                    statePath: 'hello',
                                  },
                                },
                              ],
                            },
                          },
                        ],
                    },
                },
                {
                    first: 'Jane',
                    last: {
                        statePath: 'lastName',
                    },
                },
            ],
        },
        children: 'hi',
    },
];

function traverse(item, key) {
  if (typeof item === 'object' && !Array.isArray(item) && item !== null) {
    // Object
    for (let itemKey in item) {
      if (itemKey === key) {
        console.log('found the key: ' + itemKey + ' With value: ' + item[itemKey]);
        
        // not sure what you want the end "return" of the func to be, I'm returning the value.  You could return true here instead, you could return a reference to the parent object, lots of possibilities
        return item[itemKey];
      }
      var found = traverse(item[itemKey], key);
      if (found !== undefined) return found;
      // otherwise keep looking
    }
  } else if (Array.isArray(item)) {
    // Array
    for (let i = 0; i < item.length; ++i) {
      var found = traverse(item[i], key);
      if (found !== undefined) return found;
    }
  }
}

var value = traverse(data, 'statePath');
console.log("value is " + value);

Awesome! Thank you James for your great answer! This helps me a lot!

Nenad Vracar · Accepted Answer · 2018-08-23 16:52:58Z

1

You could use for...in and store result in one var and then check that var before you call function again and break loop if value is found.

const data = [{"id":"2144d998-4c33-4b03-93d2-f6c675b24508","statePath":"div","props":{"className":"testing","name":[{"first":"John","last":{"statePath":"lastName","anArray":[{"anObject":{"anotherArray":[{"doesItWork":{"statePath":"hello"}}]}}]}},{"first":"Jane","last":{"statePath":"lastName"}}]},"children":"hi"}]

function traverse(item, key) {
  let result = false;

  for (var i in item) {
    if (i == key) {
      result = true;
      break;
    }
    if (typeof item[i] == 'object' && !result) {
      result = traverse(item[i], key)
    }
  }

  return result
}

console.log(traverse(data, 'statePath'))

answered Aug 23, 2018 at 16:52

Nenad Vracar

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1 Comment

Chris Frank Over a year ago

Wow! Very clean solution! Thank you so much!

Илья Зелень · Accepted Answer · 2018-08-23 17:26:51Z

0

My variant:

const data = [{id: '2144d998-4c33-4b03-93d2-f6c675b24508', element: 'div', props: {className: 'testing', name: [{first: 'John', last: {statePath3: 'lastName', anArray: [{anObject: {anotherArray: [{doesItWork: {statePath1: 'hello',},},],},},],},}, {first: 'Jane', last: {statePath: 'lastName',},},],}, children: 'hi',},];

function traverse(data, find) {
  for (let k in data) {
    let deepHaveKey = typeof data[k] === 'object' && traverse(data[k], find)
    
    if (find === k || deepHaveKey)
      return true
  }
  
  return false
}

console.log(traverse(data, 'statePath')); // true
console.log(traverse(data, 'state')); // false

edited Aug 23, 2018 at 17:26

answered Aug 23, 2018 at 16:59

Илья Зелень

8,2783 gold badges48 silver badges59 bronze badges

1 Comment

Chris Frank Over a year ago

Thank you for your answer Ilya! I appreciate it!

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