Apply delta to javascript array

#1

Is there any utility to apply delta object of Y.Array Event to javascript array. For example I get this delta object in Y.Array observer:

[
    {
        "retain": 1
    },
    {
        "insert": [
            {
                "copytext": "Hello world",
                "id": "1104",
            }
        ]
    },
    {
        "retain": 1
    },
    {
        "delete": 1
    }
]

So we have an array where we leave one element, then insert new, then leave one and then delete one. This is a sequence of actions that should be applied to a regular JavaScript array. What is the best way to do that?

#2

Hi, welcome.

I’m not aware of a built-in utility to apply delta objects to normal Javascript arrays, but you can define it yourself like this:

const applyDelta = (input, delta) => {
  let cursor = 0
  let output = []

  delta.forEach(op => {
    if (op.delete) {
      cursor += op.delete
    }
    else if (op.retain) {
      output.push(...input.slice(cursor, cursor + op.retain))
      cursor += op.retain
    }
    else if (op.insert) {
      output.push(...op.insert)
    }
  })

  output.push(...input.slice(cursor))

  return output
}

console.log(applyDelta(['a', 'b', 'c'], [
  {
    "retain": 1
  },
  {
    "insert": [
      {
        "copytext": "Hello world",
        "id": "1104",
      }
    ]
  },
  {
    "retain": 1
  },
  {
    "delete": 1
  }
]))

Result:

['a', { copytext: 'Hello world', id: '1104' }, 'b' ]
#3

Looks good. Thank you!