sum three different array if their name match

Question

This is my 3-array object. I want to sum the array if the year match. I want to add 3 different array if their year match the result like this

[{ year: 2011, val: 6}, {year: 2012, val: 8}, { year: 2013, val: 8 }, {year: 2014, val: 3}]

Here are my arrays:

var array1 =   {
    year: 2011,
    val: 1,
  },
  {
    year: 2012,
    val: 2,
  },
  {
    year: 2013,
    val: null,
  }]

var array2 =   {
    year: 2011,
    val: 2,
  },
  {
    year: 2012,
    val: 4,
  },
  {
    year: 2013,
    val: 5,
  }]

var array3 =   {
    year: 2011,
    val:3,
  },
  {
    year: 2012,
    val: 2,
  },
  {
    year: 2013,
    val: 3,
  },
 {
    year: 2014,
    val: 3,
 }
]