针对每个请求，将对象添加到Node.js中JSON文件中的数组中

Question

I have an image on the frontend. When the user right clicks on the image, the coordinates of that point are stored in a variable and that variable is then sent to the node server using AJAX post request. Then in the server side I am storing the x,y coordinates into a file as objects. I want to keep on piling up the set of x,y coordinates into that same file as different objects from the previous, when the user right clicks at other places on the image. The problem is that when I right click on some other position, the coordinates of that point are replacing the previous ones in the file, instead of adding to the file and keeping the previous ones as well. How can I achieve that?

.post(function(request, response){
    console.log("Request received");
    var util = require('util');
    var coordinates = request.body;
    var imageCoordinates = JSON.stringify(coordinates);
    fs.writeFile('coords.json', imageCoordinates, finished);

    function finished(err){
        console.log('all set.');
    }

    console.log('coords are:', coordinates);        
    response.send("All OK");
}); 

This is the request handler function in my server.js file.

Answer 1

fs.writeFile: Asynchronously writes data to a file, replacing the file if it already exists.

fs.appendFile: Asynchronously append data to a file, creating the file if it does not yet exist.

Answer 2

Code has two issues,

use appendFile instead of writeFile, modified the code below. Also you need to send the response once the write is completed.

function finished(err){ console.log('all set.'); response.send("All OK"); }

Otherwise response might go earlier before the write is completed.

.post(function(request, response){
    console.log("Request received");
    var util = require('util');
    var coordinates = request.body;
    var imageCoordinates = JSON.stringify(coordinates);
    fs.appendFile('coords.json', imageCoordinates, finished);

    function finished(err){
        console.log('all set.');
        response.send("All OK");
    }

    console.log('coords are:', coordinates);        

});