How to synchronously call a set of functions in javascript

Question

I am working on a javascript project that needs to get some data and process it, but I am having trouble with the asynchronous nature of JavaScript. What I want to be able to do is something like the following.

//The set of functions that I want to call in order
function getData() {
    //gets the data
}

function parseData() {
    //does some stuff with the data
}

function validate() {
    //validates the data
}

//The function that orchestrates these calls 
function runner() {
    getData();
    parseData();
    validate();
}

Here I want each function to wait for completion before going on to the next call, as I am running into the situation where the program attempts to validate the data before it has been retrieved. However, I also want to be able to return a value from these functions for testing, so I can't have these functions return a boolean value to check completion. How can I make javascript wait on the function to run to completion before moving on to the next call?

Answer 1

Use promises:

//The set of functions that I want to call in order
function getData(initialData) {
  //gets the data
  return new Promise(function (resolve, reject) {
    resolve('Hello World!')
  })
}

function parseData(dataFromGetDataFunction) {
  //does some stuff with the data
  return new Promise(function (resolve, reject) {
    resolve('Hello World!')
  })
}

function validate(dataFromParseDataFunction) {
  //validates the data
  return new Promise(function (resolve, reject) {
    resolve('Hello World!')
  })
}

//The function that orchestrates these calls 
function runner(initialData) {
    return getData(initialData)
        .then(parseData)
        .then(validate)
}

runner('Hello World!').then(function (dataFromValidateFunction) {
    console.log(dataFromValidateFunction);
})

Not only are they easy to grasp, it makes total sense from a code readability stand point. Read more about them here. If you are in a browser environment, I recommend this polyfill.