How to go about mapping an array object within an object using prototype?

Question

I have some issues with getting prototype map function to work with my array object inside my object. I get the error "x() is not a function". I know that you cant use prototype on objects but arrays within objects should be reachable using obj.arr.map().

Here is my code:

let data = [

{'a':1, 'b':2, 'c':3},
{'a':4, 'b':5, 'c':6},
{'a':7, 'b':8, 'c':9}

]

let mapped = data.map(function(data){

  let newMap = {}
  newMap['a']=data['a']
  newMap['b']=data['b']
  return newMap;

});

Mapping.prototype.protoMap = function(){

//I have tried writing it as map.data

  let protoMap = map.map(function(map){

    let protoMap1 = {}

    protoMap1['a'] = map.mappedData['a']

    return protoMap1;

  });

}

function Mapping(data = []){

  this.mappedData = data

};

let map = new Mapping(mapped);

Answer 1

Try to stay away from using global variables:

Mapping.prototype.protoMap = function() {
  // DON'T do this
  // plus, this really doesn't make sense
  // because `map` refers to the new `Mapping` object that
  // you created; what you probably want to do is use the `mappedData`
  // property on your newly created `Mapping` object
  // const protoMap = map.mappedData.map(function(map) {...})

  // instead, use `this` to access the `mappedData` property
  // that you passed to the constructor
  const protoMap = this.mappedData.map(function(item) {...})
}
const map = new Mapping(mapped)

See comments in the code snippet to figure out how to fix your example.

function Mapping(data = []) {
  this.mappedData = data
}
Mapping.prototype.protoMap = function() {
  // access the `mappedData` that was passed
  // to the `Mapping` constructor using `this`
  const protoMap = this.mappedData.map(
    function(item) {
      // use `item` argument for the `mappedData.map`
      // callback to access each item inside `mappedData`
      // individually
      const temp = {}
      temp["a"] = item["a"]
      return temp
    }
  )
  return protoMap
}

const data = [
  {'a': 1, 'b': 2, 'c': 3},
  {'a': 4, 'b': 5, 'c': 6},
  {'a': 7, 'b': 8, 'c': 9}
]

const mapped = data.map(
  function(data) {
    const newMap = {}
    newMap['a']=data['a']
    newMap['b']=data['b']
    return newMap;
  }
)

const mapping = new Mapping(mapped)
const result = mapping.protoMap()

console.log('result', result)