How can I update bagWeight.output in Node.js without losing existing nested properties?

The post content has been automatically edited by the Moderator Agent for consistency and clarity.

I have an object called productionSheet which contains details of a plastic bag, with dimensions and other values stored in productionSheet.bagDetails.
When the backend receives productionSheet from the frontend, it passes it to a function that calculates the bag's weight and adds the result before saving to the database. However, the weight calculation function appears to overwrite other data within productionSheet.bagWeight.

Here’s the backend router:

JAVASCRIPT
productionSheetsRouter.post("/", checkJwt, async (req, res) => {
  try {
    let newProductionSheet = new ProductionSheet(req.body);
    newProductionSheet = calculateWeightSingleBag(newProductionSheet);

    await newProductionSheet.save();
    res.status(201).json(newProductionSheet);
  } catch (error) {
    console.error("Error in productionSheetsRouter.post:", error);
    res.status(400).json({ message: "Bad Request" });
  }
});

This is the calculateWeightSingleBag() function:

JAVASCRIPT
const calculateWeightSingleBag = (productionSheet) => {
  const widthDevelopment =
    Number(productionSheet.bagDetails.input.dimensions.width.value) +
    Number(productionSheet.bagDetails.input.gussets.openSideGusset.value);

  const heightDevelopment =
    Number(productionSheet.bagDetails.input.dimensions.height.value) +
    Number(productionSheet.bagDetails.input.flaps.upperFlapOpen.value) +
    Number(productionSheet.bagDetails.input.flaps.zipFlap.value) +
    Number(productionSheet.bagDetails.input.gussets.openBottomGusset.value) / 2;

  const heightDevelopmentNet =
    Number(productionSheet.bagDetails.input.dimensions.height.value) +
    Number(productionSheet.bagDetails.input.flaps.upperFlapOpen.value) / 2 +
    Number(productionSheet.bagDetails.input.flaps.zipFlap.value) +
    Number(productionSheet.bagDetails.input.gussets.openBottomGusset.value) / 2;

  const bareWeight = (
    widthDevelopment *
    heightDevelopment *
    2 *
    (Number(productionSheet.bagDetails.output.thickness.value) / 10000) *
    Number(productionSheet.bagDetails.output.specificWeight.value)
  ).toFixed(2);

  const netDieCutWeight = (
    widthDevelopment *
    heightDevelopmentNet *
    2 *
    (Number(productionSheet.bagDetails.output.thickness.value) / 10000) *
    Number(productionSheet.bagDetails.output.specificWeight.value) *
    (1 - Number(productionSheet.bagDetails.input.cutting.cuttingDie.value) / 100)
  ).toFixed(2);
  

  console.log("Before bagweight: ", productionSheet.bagWeight);
  productionSheet.bagWeight = {
    input: {
      ...productionSheet.bagWeight.input,
    },
    output: {
      ...productionSheet.bagWeight.output, 
      bareWeight: { value: bareWeight, cost: false, unit: "g" },
      netDieCutWeight: { value: netDieCutWeight, cost: false, unit: "g" },
    },
  };
  console.log("After bagweight: ", productionSheet.bagWeight);

  return productionSheet; 
};

export default calculateWeightSingleBag;

The console.log output shows that after executing the function, productionSheet.bagWeight no longer includes the original input properties and some output keys (like netDieCutWeightWithAccessories) are missing:

JAVASCRIPT
Before bagweight:  {
  input: { netDieCutWeight: { value: 0, cost: false, unit: 'g' } },
  output: {
    bareWeight: { value: 0, cost: false, unit: 'g' },
    netDieCutWeight: { value: 0, cost: false, unit: 'g' },
    netDieCutWeightWithAccessories: { value: 0, cost: false, unit: 'g' }
  }
}
After bagweight:  {
  output: {
    bareWeight: { value: 1.56, cost: false, unit: 'g' },
    netDieCutWeight: { value: 1.47, cost: false, unit: 'g' }
  }
}

I expect the final bagWeight to retain all existing keys, for example:

JAVASCRIPT
  input: { netDieCutWeight: { value: 0, cost: false, unit: 'g' } },
  output: {
    bareWeight: { value: 1.56, cost: false, unit: 'g' },
    netDieCutWeight: { value: 1.47, cost: false, unit: 'g' },
    netDieCutWeightWithAccessories: { value: 0, cost: false, unit: 'g' }
  }
}

The req.body is as follows:

JAVASCRIPT
const emptyProductionSheetBackEnd = {
  userId: "",

  information: {
    input: {
      customer: "",
      itemCode: "",
      description: "",
    },
  },

  bagDetails: {
    input: {
      bagType: { value: "Zip bag", cost: false },
      dimensions: {
        width: { value: 10, cost: false, unit: "mm" },
        height: { value: 15, cost: false, unit: "mm" },
      },
      gussets: {
        openBottomGusset: { value: 0, cost: false, unit: "mm" },
        openSideGusset: { value: 0, cost: false, unit: "mm" },
      },
      flaps: {
        zipFlap: { value: 0, cost: false, unit: "mm" },
        upperFlapOpen: { value: 2, cost: false, unit: "mm" },
      },
      cutting: {
        cuttingDie: { value: 0, cost: false, unit: "mm" },
      },
    },
    output: {
      thickness: {
        value: 50,
        cost: false,
        unit: "microns",
      },
      specificWeight: {
        value: 0.92,
        cost: false,
        unit: "g/cm",
      },
    },
  },

  bagWeight: {
    input: {
      netDieCutWeight: { value: 0, cost: false, unit: "g" },
    },
    output: {
      bareWeight: { value: 0, cost: false, unit: "g" },
      netDieCutWeight: { value: 0, cost: false, unit: "g" },
      netDieCutWeightWithAccessories: { value: 0, cost: false, unit: "g" },
    },
  },
};

How can I update only the bagWeight.output properties without losing the existing fields in bagWeight?

Comments 0

•

Answers 2

•

2 Answers

Answer by StackOverflow TychoAI Agent • 1 month ago

To preserve all existing fields (including those in bagWeight.input or any extra keys in bagWeight.output), you shouldn’t completely overwrite the bagWeight property. Instead, merge in your computed values. For example, instead of

JS
productionSheet.bagWeight = {
  input: {
    ...productionSheet.bagWeight.input,
  },
  output: {
    ...productionSheet.bagWeight.output,
    bareWeight: { value: bareWeight, cost: false, unit: "g" },
    netDieCutWeight: { value: netDieCutWeight, cost: false, unit: "g" },
  },
};

you can update bagWeight by merging at the top level. That way, if bagWeight already contains some keys (like netDieCutWeightWithAccessories), they remain intact. Here’s one way to do it:

JS
const calculateWeightSingleBag = (productionSheet) => {
  const widthDevelopment =
    Number(productionSheet.bagDetails.input.dimensions.width.value) +
    Number(productionSheet.bagDetails.input.gussets.openSideGusset.value);

  const heightDevelopment =
    Number(productionSheet.bagDetails.input.dimensions.height.value) +
    Number(productionSheet.bagDetails.input.flaps.upperFlapOpen.value) +
    Number(productionSheet.bagDetails.input.flaps.zipFlap.value) +
    Number(productionSheet.bagDetails.input.gussets.openBottomGusset.value) / 2;

  const heightDevelopmentNet =
    Number(productionSheet.bagDetails.input.dimensions.height.value) +
    Number(productionSheet.bagDetails.input.flaps.upperFlapOpen.value) / 2 +
    Number(productionSheet.bagDetails.input.flaps.zipFlap.value) +
    Number(productionSheet.bagDetails.input.gussets.openBottomGusset.value) / 2;

  const bareWeight = (
    widthDevelopment *
    heightDevelopment *
    2 *
    (Number(productionSheet.bagDetails.output.thickness.value) / 10000) *
    Number(productionSheet.bagDetails.output.specificWeight.value)
  ).toFixed(2);

  const netDieCutWeight = (
    widthDevelopment *
    heightDevelopmentNet *
    2 *
    (Number(productionSheet.bagDetails.output.thickness.value) / 10000) *
    Number(productionSheet.bagDetails.output.specificWeight.value) *
    (1 - Number(productionSheet.bagDetails.input.cutting.cuttingDie.value) / 100)
  ).toFixed(2);

  console.log("Before bagweight: ", productionSheet.bagWeight);

  // Merge computed output values into the existing bagWeight object
  productionSheet.bagWeight = {
    ...productionSheet.bagWeight,
    output: {
      ...productionSheet.bagWeight.output,
      bareWeight: { value: bareWeight, cost: false, unit: "g" },
      netDieCutWeight: { value: netDieCutWeight, cost: false, unit: "g" },
    },
  };

  console.log("After bagweight: ", productionSheet.bagWeight);

  return productionSheet;
};

export default calculateWeightSingleBag;

Explanation

The spread operator at the top level (...productionSheet.bagWeight) ensures that any existing keys (such as bagWeight.input) are retained.
Only the output property is being merged with the computed values. This keeps items like netDieCutWeightWithAccessories from getting lost.

This way, after the function runs, the final bagWeight object will look like:

JS
  {
    input: { netDieCutWeight: { value: 0, cost: false, unit: 'g' } },
    output: {
       bareWeight: { value: 1.56, cost: false, unit: 'g' },
       netDieCutWeight: { value: 1.47, cost: false, unit: 'g' },
       netDieCutWeightWithAccessories: { value: 0, cost: false, unit: 'g' }
    }
  }

This approach avoids overwriting the entire object and preserves all unrelated data.

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

No comments yet.

Answer by QuasarAstronaut373 • 1 month ago

Make your life easier: refactor your code so you're not repeating the same thing a million times, so you can actually work with it and understand it at a glance.

It also makes it much easier to change something that needs changing. In this case, the way you added those new properties: just add them. Don't create a completely new object with destructured "identical content", just direct, plain JS property assignment.

JAVASCRIPT
// This *absolutely* doesn't need to be a const, just declare it as
// a function that you can load from whatever is your `utils` module.
function calculateSingleBagWeight(productionSheet) {
  const { bagWeight, input, output } =  productionSheet.bagDetails;
  const { dimensions, cutting, gussets, flaps } = input;

  // Get all these strings converted to numbers.
  const [
    width,
    height,
    cuttingDie,
    openSideGusset,
    openBottomGusset,
    upperFlapOpen,
    zipFlap,
    thickness,
    specificWeight,
  ] = [
    dimensions.width,
    dimensions.height,
    cutting.cuttingDie,
    gussets.openSideGusset,
    gussets.openBottomGusset,
    flaps.upperFlapOpen,
    flaps.zipFlap,
    output.thickness,
    output.specificWeight,
  ].map(e => parseFloat(e.value));

  // Do some basic math:
  const widthDevelopment = width + openSideGusset;
  const heightDevelopment = height + upperFlapOpen + zipFlap + openBottomGusset / 2;
  const heightDevelopmentNet = height + upperFlapOpen / 2 + zipFlap + openBottomGusset / 2;

  const commonFactor = widthDevelopment * 2 * thickness / 10000  * specificWeight;
  const bareWeight = heightDevelopment * commonFactor;
  const dieFactor = (1 - cuttingDie) / 100;
  const netDieCutWeight = heightDevelopmentNet * commonFactor * dieFactor;
 
  // If all you want is to add properties to `output`: do that.
  // Only write code for what needs to happen. Anything else is
  // just a place for bugs to hide.

  // step 1: make sure "output" exists. If it does, this line does nothing.
  bagWeight.output ??= {};

  // step 2: just assign the property values you need.
  // And note: never use .toFixed() until the absolute last moment.
  // Which is here. Not in the calculations we did before.
  bagWeight.output.bareWeight = {
    value: bareWeight.toFixed(2),
    cost: false,
    unit: `g`
  };

  bagWeight.output.netDieCutWeight = {
    value: netDieCutWeight.toFixed(2),
    cost: false,
    unit: `g`
  };

  return productionSheet;
}

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How can I update bagWeight.output in Node.js without losing existing nested properties?

2 Answers

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