Add option to filter values that should be skipped

[maximilianschmitt]

I have a use case where I'm using flat on data that has 'meta' objects as leafs. With a filter function, I could tell flat to ignore these meta-leafs, no matter how deep they're nested.

[marcincichocki]

Awesome, I was looking for something exactly like this. I hope this will get merged. +1

[maximilianschmitt]

@hughsk have you had time to check this out? Would be really great to have this merged. Please let me know if there's anything missing. Thanks!

[kristianmandrup]

I also need this. I would also like those not to be flattened to still be added to result object, just not with a nested key. Looking for something like this:
Would it be possible with this fix/PR?

Flatten example

let obj = {
  x: {
    a: {
      b: [{name: hello}]
      c: {
        name: 'hello'
        status: 'done'
      }
    }
  },
  y: [],
  v: 'hello'
}

// 
let keepOrFlat = function(node) {
  if (node.name && typeof node.name === 'string') return true
  if (Array,isArray(node)) return true
  if (typeof node === 'object') return false
  return true
}

let flatten = function(node) {
  if (typeof node !== 'object') return false  
  if (node.name) return false
  return true
}

let keep = function(node) {
  if (typeof node !== 'object') return true  
  if (node.name && typeof node.name === 'string') return true
}

// if keepOrFlat is set, other condition functions are ignored
let conditions = {
  keepOrFlat, 
  flatten, 
  keep 
}

let flatObj = obj.flatten({
  sep: '.', 
  conditions 
})

let obj = {
  'x.a.b': [],
  'x.a.c': {
    name: 'hello',
  },
  y: [],
  v: 'hello'
}