How to use a variable from a json to call another json in preload() function?

Question

I am using using p5js library in javascript. I used wrapAPI to make some custom APIs to grab posts and comments from the web.

The first API returns the latest posts with the post ID. The second API returns comments of the post with the ID from the first API call.

What is a good way to do this?

My idea is to replace idvox and categoria inside preload() with:

idvox = datav.data.vox[1].idvox;

but the second loadJSON() function does not work. If I try to console.log or call the variable with the post id an empty Object or undefined value is returned.

function preload(){

    var datav = loadJSON('https://wrapapi.com/use/example/example/example/latest?wrapAPIKey=API_KEY');
    categoria = datav.data.vox[1].category;
    idvox = datav.data.vox[1].idvox;
    dataC = loadJSON('https://wrapapi.com/use/example/example/example/0.0.5?categoria='+categoria+'&idvox='+idvox+'&wrapAPIKey=API_KEY');
}

Charlie Wallace · Accepted Answer · 2019-03-29T13:19:05.463

In order to use data from one loadJSON call as parameters in a second call you will need to take into consideration that these are asynchronous calls. See Loading-external-files:-AJAX, -XML, -JSON

Instead of directly setting a variable to the return value you will unload the data in a call back function:

Callbacks

A callback is a function that is passed to another function as a parameter, and called by that other function. A callback function is useful when working with asynchronous functions because it allows us to specify some code to execute after the first asynchronous task has completed.

We've actually already used callbacks when we used setTimeout, setInterval, and addEventListener. For example, "doSomething" below is a callback function:

function doSomething() {
  console.log("doing something!");
}

setTimeout(doSomething, 5000);

You will see callbacks used in p5.js and jQuery to tell the program what to do after the external data is received.

function setup() {
  loadJSON("data.json", drawData);
}

loadJSON

loadJSON loads a JSON file and returns a JavaScript object. It takes two arguments, the path to the file, and the callback function. When the server has returned the JSON data and it has been parsed, drawData is run with the result automatically passed in as the variable "data".

function drawData(data) {
  // person 1 bubble
  fill(155, 30, 180, 180);
  ellipse(250, 200, data.person1.age * 5, data.person1.age * 5); // person1.age = 30
  fill(255);
  text(data.person1.name, 210, 200); // person1.name = Morgan

  // person 2 bubble
  fill(180, 180, 34, 180);
  ellipse(350, 200, data.person2.age * 5, data.person2.age * 5); // person2.age = 32
  fill(255);
  text(data.person2.name, 330, 200); // person2.name = Joss
}

For your purposes you will adapt code like this to chain your AJAX calls. In your case you will have a function that makes the second call and you will pass it to the first call to loadJSON. The second call will also pass in a callback function which you will use to unload your final data.

Thanks you so much! Passing a function as argument after the JSON worked! — TMX, Mar 29 '19 at 17:28
Great, you can upvote this answer if it is helpful. Here is some info on accepting and upvoting https://stackoverflow.com/help/someone-answers The idea is to make good answers visible to others with similar questions. — Charlie Wallace, Mar 29 '19 at 17:48

How to use a variable from a json to call another json in preload() function?

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