Javascript object retaining "old" properties, can't override?

Question

I have the following code:

    const readDataFromSql = () => {
        // going to have to iterate through all known activities + load them here
        let sql = "[...]"
        return new Promise((resolve, reject) => {
            executeSqlQuery(sql).then((dict) => {
                let loadedData = [];
                for (let key in dict) {
                    let newItemVal = new ItemVal("reading hw", 7121, progress.DONE);
                    loadedData.push(newItemVal);
                }
                resolve(loadedData);
            });
        });
    }

ItemVal implementation:

class ItemVal {
   constructor(name, time, type) {
      this.name = name
      this.time = time
      this.type = type 
   }
}

Let's assume that newItemVal = "reading hwj", 5081, progress.PAUSED when readDataFromSql() first runs.

readDataFromSql() is then again called after some state changes -- where it repulls some information from a database and generates new values. What is perplexing, however, is that when it is called the second time, newItemVal still retains its old properties (attaching screenshot below).

Am I misusing the new keyword?

Answer 1

From what I can see in your example code, you are not mutating existing properties but creating a new object with the ItemVal constructor function and adding them to an array, that you then return as a resolved promise. Are you sure the examples you give a correct representation of what you are actually doing

Given that, I'm not sure what could be causing the issue you are having, but I would at least recommend a different structure for your code, using a simpler function for the itemVal.

Perhaps with this setup, you might get an error returned that might help you debug your issue.

const itemVal = (name, time, type) => ({ name, time, type })

const readDataFromSql = async () => {
  try {
    const sql = "[...]"
    const dict = await executeSqlQuery(sql)

    const loadedData = dict.map((key) =>
      ItemVal("reading hw", 7121, progress.DONE)
    )

    return loadedData
 

  } catch (error) {
    return error
  }
};

If the issue is not in the function, then I would assume that the way you handle the data, returned from the readDataFromSql function, is where the issue lies. You need to then share more details about your implementation.