Kurapati Mahesh

Posted on Jul 15, 2022

Find path in given object

#javascript #webdev #beginners #programming

// Problem:

/*
- Write method findPath
- Should take two params:
    - object
    - keys separated by dots as string
- Return value if it exists at that path inside the object, else return undefined
*/

var obj = {
    a: {
        b: {
            c: 12,
            j: false
        },
        k: null
    }
};

// Solution:

const findPath = (object, path) => {
    let i=1;
    const pathList = path.split('.');
    let obj = object[pathList[0]];
    while(i<pathList.length) {
        if(typeof obj === 'object') {
            obj = obj[pathList[i]];
            i++;
        } else {
            return undefined;
        }
    }
    return obj;
};

// cases
console.log(findPath(obj, 'a.b.c')); // 12
console.log(findPath(obj, 'a.b')); // {c: 12, j: false}
console.log(findPath(obj, 'a.b.d')); // undefined
console.log(findPath(obj, 'a.c')); // undefined
console.log(findPath(obj, 'a.b.c.d')); // undefined
console.log(findPath(obj, 'a.b.c.d.e')); // undefined
console.log(findPath(obj, 'a.b.j')); //false
console.log(findPath(obj, 'a.b.j.k')); //undefined
console.log(findPath(obj, 'a.k')); //null

thanks

Top comments (19)

Alex Lohr • Jul 15 '22

Recursion makes for a simpler solution:

const findPath = (obj, path) => {
  const [item, nextPath] = /([^\.]+)\.(.*)/.exec(path)?.slice(1, 3) || [path];
  return nextPath ? findPath(obj?.[item], nextPath) : obj?.[item];
}

Calin Baenen • Jul 16 '22

As Frank Wisniewski suggests, try Optional Chaning.
It works on more than just object properties as well. It also lets you optionally call functions.

Kurapati Mahesh • Jul 16 '22

Yes. Optional chaining is latest feature and might not be used (or enabled) everywhere. If someone is using then cool otherwise we need to follow traditional way.

Jon Randy 🎖️ • Jul 15 '22

This confused me initially because of the function name - I thought we were going to find a path to a property with a given value, but we're actually doing the opposite. A better name might be getPropertyWithPath

Kurapati Mahesh • Jul 16 '22

findPath similar to getPropertyPath. I hope people would get it as I am referring to object.

Frank Wisniewski • Jul 15 '22

Does that really make sense?

console.log(
  obj.a?.b?.c?.d
)
// or
console.log(
  obj.a?.b
)

gives the same result

Calin Baenen • Jul 16 '22

True, but I þink ðis is more for backwards compatibility.
But yes, newer code should probably use Optional Chaining.

Kurapati Mahesh • Jul 16 '22

Yes. Optional Chaining is the best and more readable.

Jon Randy 🎖️ • Jul 16 '22

But this isn't really doing the same thing? It's not dynamic

Frank Wisniewski • Jul 16 '22

I don't understand what you mean by that..

Kurapati Mahesh • Jul 15 '22

This could be an impossible case as no one could assign key as dot. Anyhow, my solution is to cover the use cases mentioned.

Calin Baenen • Jul 16 '22 • Edited

I think you forgot you can format objects like JSON (JavaScript Object Notation):

let my_obj = {
    "foo": "bar",
    ".":   "baz"
}

Kurapati Mahesh • Jul 16 '22

I was referring to real world scenario. No one uses any object key as dot alone.

Usually, programmers give readable key name based on their requirement.

Everything has its corner cases, I am generalizing concept to find the path. It is not that I need to cover all worst cases.

Hope you guys get it. Also, it would be better if you guys provide solution for the case you are mentioning. That might worth for the people came across this article.

Thank you.

FJones • Jul 16 '22

The simplest solution would be to do away with split and instead consider a token-based approach:

"." refers to a field called "." on the root, whereas "foo.." refers to a field called "." on the nested object at root-key "foo". And then "foo...bar" refers to a foo->.->bar path.

However, this also causes some ambiguity: foo.....bar could be either foo->.->.->bar or foo->...->bar.

A generalized solution would then use escape sequences. e.g. \. for a dot literal, \\ for a backslash literal, but that naturally makes parsing the path ever so more complex.

Calin Baenen • Jul 16 '22

I like ðis approach.
Sure it requires some more complexity and probably takes longer (but not too much) than .split(char_seq) but it gets ðe job done and better.

However, this also causes some ambiguity: foo.....bar could be either foo->.->.->bar or foo->...->bar.

Ðis could be solved by checking ðe more specific case (foo->.->.->ba) first and if ðat fails try ðe simpler one(s).
Of course it won't be perfect but it can at least try to figure out intentions.