JavaScript: Executing synchronously

I am being ask this question often; therefore, I am posting the answer here.

Commonly there are those who wish to do a process that normally is asynchronously, such as performing AJAX operations in a synchronous fashion. There are a few ways to do this.

If you are coding in JS for NodeJS, then you can use the package async-waterfall, example:

  function readFile(callback) {
        fs.readFile('your_file.json', function (error, file) {
            if (error) {
                callback(error);
            } else {
                callback(null, file);
            }
        });
    }
    ...
    function processFile(file, callback){
        // Some code here
    }
    ...
    async.waterfall([
        readFile,
        processFile
    ], function (error) {
        if (error) {
            // handle error made in readFile or processFile method 
        }
    });

Else, you can use promise chains which is part of Javascript, example:

    new Promise(function(resolve, reject) {
      try{
          resolve(readfile());
      }catch(e){
          reject("error message");
      }
    }).then(function(result) {
      return processFile(result)    
    });

Or, you can use async/await: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function

© 2018, Alejandro G. Carlstein Ramos Mejia. All rights reserved.