A way to access a property without knowing its path in a nested js object

Question

is there a way to access a nested property within an object without knowing its path? For instance I could have something like this

let test1 = {
  location: {
    state: {
     className: 'myCalss'
    }
 }
};

let test2 = {
  params: {
    className: 'myCalss'
  }
};

Is there neat way to 'extract' className property? I have a solution but it's pretty ugly, and it accounts just for this two cases, I was wondering if there is something more flexible I could do

Recursively iterating over all object properties is really the only thing you can do. — Felix Kling, Jun 06 '18 at 22:53
Theoretically, you could do `JSON.stringify()` and build a regular expression to do what you're looking for. — theGleep, Jun 06 '18 at 23:00
@theGleep If you committed such code into a repository I had to work in, I would hunt you down and kill you ;) — Dexygen, Jun 06 '18 at 23:06

Patrick Roberts · Accepted Answer · 2018-06-06T23:19:51.030

Here's a somewhat elegant approach to creating nested property getters:

const getProperty = property => {
  const getter = o => {
    if (o && typeof o === 'object') {
      return Object.entries(o)
        .map(([key, value]) => key === property ? value : getter(value))
        .filter(Boolean)
        .shift()
    }
  }

  return getter
}

const test1 = {
  location: {
    state: {
      className: 'test1'
    }
  }
}

const test2 = {
  params: {
    className: 'test2'
  }
}

const test3 = {}

const getClassName = getProperty('className')

console.log(getClassName(test1))
console.log(getClassName(test2))
console.log(getClassName(test3))

If you want to prevent cyclical objects from causing a stack overflow, I suggest using a WeakSet to keep track of iterated object references:

const getProperty = property => {
  const getter = (o, ws = new WeakSet()) => {
    if (o && typeof o === 'object' && !ws.has(o)) {
      ws.add(o)
      return Object.entries(o)
        .map(([key, value]) => key === property ? value : getter(value, ws))
        .filter(Boolean)
        .shift()
    }
  }

  return getter
}

const test1 = {
  location: {
    state: {
      className: 'test1'
    }
  }
}

const test2 = {
  params: {
    className: 'test2'
  }
}

const test3 = {}
const test4 = {
  a: {
    b: {}
  }
}

test4.a.self = test4
test4.a.b.self = test4
test4.a.b.className = 'test4'

const getClassName = getProperty('className')

console.log(getClassName(test1))
console.log(getClassName(test2))
console.log(getClassName(test3))
console.log(getClassName(test4))

score 1 · Answer 2 · answered Jun 06 '18 at 22:59

Sure. Give this a try. It recursively iterate over the object and returns the first match. You can configure the for loop to match all or last, according to your needs

let test1 = {
  location: {
    state: {
     className: 'myCalss'
    }
 }
};

let test2 = {
  params: {
    className: 'myCalss'
  }
};

function getClassName(obj) {
  if(typeof obj === "object" && 'className' in obj) {
    return obj.className
  }
  const keys = Object.keys(obj)
  for(let i = 0; i < keys.length; i++) {
    let key = keys[i]
    let res = getClassName(obj[key])
    if(res) return res
  }
  return null
}

console.log(getClassName(test1), getClassName(test2))

A way to access a property without knowing its path in a nested js object

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