Direct allocation of objects in javascript

Question

how to replace objects properties without changing other properties and if uneven number of objects are allocated, copy over other properties?

I guess the question might not make any sense. The example will explain everything. Lets say I have:

var oldData = {
  fruits: fruits,
  veggies: [{
      sweet: false,
      colour: red,
      data: [1, 2, 3]
    }]
};

var newData = {
  veggies: [{
    sweet: true,
    data: [99, 100, 101]
  },
  {
    sweet: false,
    data: [888, 777, 665],
  }]
};

var standardColor = "blue";

The goal is to:

replace old veggies data with new data
replace old veggies sweet value with new sweet value
retain old veggies colour value, unless there is a new one in new data, therefore replace it.
if a following new veggies object does not have colour, use standardColor - "blue"
leave fruits untouched

Problems:

newData veggies can have more objects than oldData, therefore I would need to iterate through them somehow?

My poor attempt:

function replaceVeggies (newData) {
  oldData.veggies = newData.veggies
};

is there any primary key that you should use or the is the first element in oldData same as the first in newData, and second = second and so on? — sertsedat
– sertsedat, Commented Mar 20, 2018 at 10:15
Do you mean Object.assign() ? developer.mozilla.org/es/docs/Web/JavaScript/Referencia/… — jlvaquero
– jlvaquero, Commented Mar 20, 2018 at 10:15
@jackjop there is no primary key. I want to keep colour if there is one in old data. If old data and new data don't have colour, use standardColor. — user007
– user007, Commented Mar 20, 2018 at 10:17
@user9521814 are you sure? I think that Object.assign() acomplish the goals you posted. Read the mdn please. — jlvaquero
– jlvaquero, Commented Mar 20, 2018 at 10:23

Raul Sauco · Accepted Answer · 2018-03-20 12:41:01Z

This should work for you.

I added some extra data to test some of the requirements.

var oldData = {
  fruits: "fruits",
  veggies: [{
      sweet: false,
      colour: "red",
      data: [1, 2, 3]
    },
    {
      sweet: true,
      // colour: "red",
      data: [1, 2, 3]
    }
  ]
};

var newData = {
  veggies: [{
      sweet: true,
      data: [99, 100, 101]
    },
    {
      sweet: false,
      data: [888, 777, 665]
    },
    {
      sweet: false,
      data: [444, 558, 333]
    }
  ]
};

var standardColor = "blue";

// Iterate through the newData object
for (var i = 0; i < newData.veggies.length; i++) {

  var newVeggie = newData.veggies[i];

  // Check if the index value exists on the old array
  if (oldData.veggies[i] !== null && (typeof oldData.veggies[i] !== "undefined")) {

    // Always replace data
    oldData.veggies[i].data = newVeggie.data;

    // Always replace sweet value
    oldData.veggies[i].sweet = newVeggie.sweet;

    // Replace colour if exists in new data
    if (newVeggie.colour !== undefined) {

      oldData.veggies[i].colour = newVeggie.colour;

    } else {

      // If old data didn't have colour value set default
      if (oldData.veggies[i].colour == undefined) {
        oldData.veggies[i].colour = standardColor;
      }

    }

  } else {

    // Check if the colour is null
    if (newData.veggies[i].colour == undefined) {

      newData.veggies[i].colour = standardColor;

    }

    // Assign the new veggie directly
    oldData.veggies[i] = newVeggie;
  }

  console.log("Veggie " + i);

  // Iterate over the properties
  Object.keys(oldData.veggies[i]).forEach(function(key) {

    console.log("  " + key + ": " + oldData.veggies[i][key]);

  });
}

A. Bandtock · Accepted Answer · 2018-03-20 10:34:08Z

1

The JS builtin Object.assign takes care of this for you:

const x = {
  y: 10,
  z: 20
}

console.log(JSON.stringify(x))

console.log(JSON.stringify(Object.assign(x, { y : 30, a: 45 })))

edited Mar 20, 2018 at 10:34

answered Mar 20, 2018 at 10:24

A. Bandtock

1,2519 silver badges14 bronze badges

3 Comments

user007 Over a year ago

I comprehend the allocation itself. The problem lies with "newData veggies can have more objects than oldData, therefore I would need to iterate through them somehow?" And also being mindful of "retaining old veggies colour value if no new colour is present and if no colour in old or new data, use standard colour"

A. Bandtock Over a year ago

Object.assign takes care of all that for you, it'll take all values from the second parameter and override/add them to the first parameter. So you'd simply call it first with const result = Object.assign(oldData, newData) then pass it through to Object.assign(defaults, resultOfFirstCall)

A. Bandtock Over a year ago

Edited the answer to more accurately reflect what you were asking.

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