Importing d3.JS JSON data without polluting the global scope

Question

Importing d3.JS JSON data without polluting the global scope

Here is a JSON object:

{
    "temp_data": [10,15,20]
}

I'm trying to import it:

var temp_data;
//Importing from JSON
if(true){
    d3.json("graph.json", function(error, graph) {
        if (error){
            throw error;
        }
        temp_data = graph.temp_data;
        console.log(temp_data);    //successfully logs data
    });
}

console.log("temp: " + temp_data); //Cannot retrieve data

The issue is that even though temp_data is declared as a global variable, the second log does not display the data.

javascript json d3.js

Answer 1

Answer №1

When you pass a callback function to d3.json(), it runs asynchronously. This can lead to situations where your second console.log() executes before the "graph.json" file has been fetched, resulting in your global variable not being populated yet. To avoid this, it is important to perform any operations with the retrieved data inside the callback function itself.

Answer 2

When you pass a callback function to d3.json(), it runs asynchronously. This can lead to situations where your second console.log() executes before the "graph.json" file has been fetched, resulting in your global variable not being populated yet. To avoid this, it is important to perform any operations with the retrieved data inside the callback function itself.

Answer 3

Answer №2

Adding on to the information provided in the answer that was accepted: if you hold off for a brief moment, you can utilize your console.log outside of the callback:

setTimeout(function(){
    console.log("Outside of the callback: " + temp_data);
}, 1000);

Take a look at this plunker: https://plnkr.co/edit/zTg6Y6KSVedIBT2tVCu9?p=preview

The explanation for this was already covered in the accepted answer: due to its asynchronous nature, the code after d3.json executes almost immediately, without waiting for the completion of d3.json.

Answer 4

Adding on to the information provided in the answer that was accepted: if you hold off for a brief moment, you can utilize your console.log outside of the callback:

setTimeout(function(){
    console.log("Outside of the callback: " + temp_data);
}, 1000);

Take a look at this plunker: https://plnkr.co/edit/zTg6Y6KSVedIBT2tVCu9?p=preview

The explanation for this was already covered in the accepted answer: due to its asynchronous nature, the code after d3.json executes almost immediately, without waiting for the completion of d3.json.

Importing d3.JS JSON data without polluting the global scope

Answer №1

Answer №2

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