How do I implement data range filtering in Typescript?

Question

How do I implement data range filtering in Typescript?

Seeking assistance with filtering data by date range and forwarding the results to the client. The objective is to extract tickets created within specific dates, but I keep encountering a console error which is proving challenging to resolve.

    var before:Date = req.query.before;
  if(before !== undefined){
        //@ts-ignore
        var after:Date = req.query.before;
        var filteredData = tempData.filter(function(t){
        return res.send(new Date(t.creationTime) >= after && new Date(t.creationTime) <= before);      
        });
  }

This is the error message displayed in the console:

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at ServerResponse.setHeader (_http_outgoing.js:558:11)
    at ServerResponse.header (C:\Project\server\node_modules\express\lib\response.js:771:10)
    at ServerResponse.json (C:\Project\server\node_modules\express\lib\response.js:264:10)
    at ServerResponse.send (C:\Project\server\node_modules\express\lib\response.js:158:21)
    at C:\Project\server\index.ts:48:20
    at Array.filter (<anonymous>)
    at C:\Project\server\index.ts:47:37
    at Layer.handle [as handle_request] (C:\Project\server\node_modules\express\lib\router\layer.js:95:5)
    at next (C:\Project\server\node_modules\express\lib\router\route.js:137:13)  
    at Route.dispatch (C:\Project\server\node_modules\express\lib\router\route.js:112:3)

typescript express date http filter

Answer 1

Answer №1

Each element in the tempData array is evaluated by the function provided to the filter method.

Within the filter function, there is a call to the res.send() method which sends a response back to the client. It's important to note that this method should only be called once per request, but currently, it is being called for each element in the tempData array.

To optimize your code, consider filtering the data first before sending it back to the client.

let filteredData = tempData.filter(function(t){
    return new Date(t.creationTime) >= after && new Date(t.creationTime) <= before;
});
res.send(filteredData);

In addition, there seems to be an issue with your code where both the before and after variables are set to req.query.before.

The statement

new Date(t.creationTime) <= before && new Date(t.creationTime) >= after;

will likely result in yielding false unless t.creationTime equals req.query.before, leading to an empty array for filteredData. Refer to the documentation on the filter method for more insights.

A possible solution (assuming req.query.after is defined) could be:

const before:Date = req.query.before;
  if(before !== undefined){
        //@ts-ignore
        const after:Date = req.query.after;
        let filteredData = tempData.filter(function(t){
          return new Date(t.creationTime) <= before && new Date(t.creationTime) >= after;
      });
      TICKETS_AMOUNT = filteredData.length.toString();
      res.send(filteredData);
  }

I have provided a full example below:

interface DataType {
    name: string,
    date: Date,
}

let data: Array<DataType> = [
    {"name": "foo", date: new Date(2020, 5, 12)},
    {"name": "bar", date: new Date(2020, 7, 20)},
    {"name": "baz", date: new Date(2021, 2, 23)},
];

app.get('/filter-date-range', (req, res): void => {
    let result = data;

    if (req.query.before) {
        let before: Date = new Date(String(req.query.before));
        if (!isNaN(before.getTime())) {
            result = result.filter((e) => e.date <= before);
        } else {
            res.status(400).send("Unable to parse before date.");
            return;
        }
    }

    if (req.query.after) {
        let after: Date = new Date(String(req.query.after));
        if (!isNaN(after.getTime())) {
            result = result.filter((e) => e.date >= after);
        } else {
            res.status(400).send("Unable to parse after date.");
            return;
        }
    }

    res.json(result);
});

Simply adjust the data variable to suit your specific project needs.

Answer 2

Each element in the tempData array is evaluated by the function provided to the filter method.

Within the filter function, there is a call to the res.send() method which sends a response back to the client. It's important to note that this method should only be called once per request, but currently, it is being called for each element in the tempData array.

To optimize your code, consider filtering the data first before sending it back to the client.

let filteredData = tempData.filter(function(t){
    return new Date(t.creationTime) >= after && new Date(t.creationTime) <= before;
});
res.send(filteredData);

In addition, there seems to be an issue with your code where both the before and after variables are set to req.query.before.

The statement

new Date(t.creationTime) <= before && new Date(t.creationTime) >= after;

will likely result in yielding false unless t.creationTime equals req.query.before, leading to an empty array for filteredData. Refer to the documentation on the filter method for more insights.

A possible solution (assuming req.query.after is defined) could be:

const before:Date = req.query.before;
  if(before !== undefined){
        //@ts-ignore
        const after:Date = req.query.after;
        let filteredData = tempData.filter(function(t){
          return new Date(t.creationTime) <= before && new Date(t.creationTime) >= after;
      });
      TICKETS_AMOUNT = filteredData.length.toString();
      res.send(filteredData);
  }

I have provided a full example below:

interface DataType {
    name: string,
    date: Date,
}

let data: Array<DataType> = [
    {"name": "foo", date: new Date(2020, 5, 12)},
    {"name": "bar", date: new Date(2020, 7, 20)},
    {"name": "baz", date: new Date(2021, 2, 23)},
];

app.get('/filter-date-range', (req, res): void => {
    let result = data;

    if (req.query.before) {
        let before: Date = new Date(String(req.query.before));
        if (!isNaN(before.getTime())) {
            result = result.filter((e) => e.date <= before);
        } else {
            res.status(400).send("Unable to parse before date.");
            return;
        }
    }

    if (req.query.after) {
        let after: Date = new Date(String(req.query.after));
        if (!isNaN(after.getTime())) {
            result = result.filter((e) => e.date >= after);
        } else {
            res.status(400).send("Unable to parse after date.");
            return;
        }
    }

    res.json(result);
});

Simply adjust the data variable to suit your specific project needs.

Answer 3

Answer №2

Each element in the tempData array will undergo evaluation by the function passed to the filter method.

I made a modification, and now I no longer receive console errors; however, there seems to be no output as a result.

const before: Date = req.query.before;
if(before !== undefined){
    //@ts-ignore
    const after: Date = req.query.before;
    let filteredData = tempData.filter(function(t){
        return new Date(t.creationTime) <= before && new Date(t.creationTime) >= after;
    });
    TICKETS_AMOUNT = filteredData.length.toString();
    res.send(filteredData);
}

Answer 4

Each element in the tempData array will undergo evaluation by the function passed to the filter method.

I made a modification, and now I no longer receive console errors; however, there seems to be no output as a result.

const before: Date = req.query.before;
if(before !== undefined){
    //@ts-ignore
    const after: Date = req.query.before;
    let filteredData = tempData.filter(function(t){
        return new Date(t.creationTime) <= before && new Date(t.creationTime) >= after;
    });
    TICKETS_AMOUNT = filteredData.length.toString();
    res.send(filteredData);
}

How do I implement data range filtering in Typescript?

Answer №1

Answer №2

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