title: merge objects in same array based on common value in Javascript
body: <p>I have an array: </p>
  
  <pre><code>[
    {
      assignmentId:17,
      email:"john.smith@email.com"
      expectation: "Make sure to proofread!",
      firstName:"John"
      id:23
      ignoreForFeedback: true
      lastName:"Smith"
      level:2
      levelFraction:null
      score:35
    },
    {
      assignmentId:17
      countsPerCategory: Array(4)
      email:"john.smith@email.com"
      firstName:"John"
      frequentErrors: Array(5)
      id:23
      ignoreForGrading: true
      lastName:"Smith"
    },
    {
      assignmentId:17,
      email:"cl@email.com"
      expectation: "cite sources",
      firstName:"Cindy"
      id:45
      ignoreForFeedback: true
      lastName:"Lee"
      level:2
      levelFraction:null
      score:32
    },
    {
      assignmentId:17
      countsPerCategory: Array(4)
      email:"cl@email.com"
      firstName:"Cindy"
      frequentErrors: Array(5)
      id:45
      ignoreForGrading: true
      lastName:"Lee"
    }
  ]
  </code></pre>
  
  <p>I want to combine the Objects with the same 'id' into the same object within the array. Their common keys should also be combined (eg: 'firstName', 'email'). Can someone suggest the best way to do this? Either with ES6 or Lodash</p>