Running JavaScript code without blocking the main thread

Question

Running JavaScript code without blocking the main thread

While studying JavaScript and JSON, I encountered some issues. I have a script that functions with JSON data, but the performance of my code is not optimal. The code only works when I debug it step by step using tools like Firebug which leads me to conclude that the execution time (especially the part related to creating the table) is too long, causing the browser to halt.

Below is the problematic section of the code:


// Javascript code block where JSON data is processed

The main concern is that the code responsible for generating the table does not wait for the JSON processing code to finish executing. How can I address this issue? I would prefer a simple solution without utilizing jQuery or callbacks since I am still a beginner in programming

javascript ajax asynchronous time-complexity

Answer 1

Answer №1

To make it function properly, you need to rearrange some code. Initially, break it down into functions for easier handling. The process begins by loading the arrayEntita first. Once that is complete, the other two arrays are filled. Finally, when all arrays are populated, the table is constructed.

 var arrayCarte = [];
 var arrayEntita = [];
 var arraycardbyuser = [];
 function displayArrayCards() {
    var richiestaEntity = new XMLHttpRequest();
        richiestaEntity.onreadystatechange = function () {
             if (richiestaEntity.readyState == 4) {
             var objectentityjson = {};
             objectentityjson = JSON.parse(richiestaEntity.responseText);

              arrayEntita = objectentityjson.cards;
              BuildArrayEntita();
            }
        }
        richiestaEntity.open("GET", "danielericerca.json", true);
        richiestaEntity.send(null);
    }

    // Rest of the JavaScript code remains the same

The condition `if (i + 1 == arrayEntita.length)` checks if all responses have been received before executing BuildTable(); otherwise, ensure that all responses are returned before calling the buildtable().

Answer 2

To make it function properly, you need to rearrange some code. Initially, break it down into functions for easier handling. The process begins by loading the arrayEntita first. Once that is complete, the other two arrays are filled. Finally, when all arrays are populated, the table is constructed.

 var arrayCarte = [];
 var arrayEntita = [];
 var arraycardbyuser = [];
 function displayArrayCards() {
    var richiestaEntity = new XMLHttpRequest();
        richiestaEntity.onreadystatechange = function () {
             if (richiestaEntity.readyState == 4) {
             var objectentityjson = {};
             objectentityjson = JSON.parse(richiestaEntity.responseText);

              arrayEntita = objectentityjson.cards;
              BuildArrayEntita();
            }
        }
        richiestaEntity.open("GET", "danielericerca.json", true);
        richiestaEntity.send(null);
    }

    // Rest of the JavaScript code remains the same

The condition `if (i + 1 == arrayEntita.length)` checks if all responses have been received before executing BuildTable(); otherwise, ensure that all responses are returned before calling the buildtable().

Answer 3

Answer №2

When making AJAX requests, it is important to remember that they are asynchronous processes. They can arrive at any time during execution and JavaScript does not wait for the server response before moving on to the next task. Although there is synchronous XHR available, it is generally not recommended as it goes against the core idea of AJAX.

To handle this asynchronous behavior, a common practice is to use a "callback" function. This function is executed at a later time, allowing you to specify when exactly you want it to run. For example, if you need to generate a table after receiving data:

function getData(callback){
    //Setting up AJAX request
    var request = new XMLHttpRequest();

    //Listening for state changes
    request.onreadystatechange = function() {

        //Checking if the request is complete and successful
        if (request.readyState === 4 && request.status === 200) {
        
            //Executing the callback function with the received data
            callback.call(this, request.responseText);
        }
    }
    request.open("GET", "data.json"); //defaults to asynchronous (true)
    request.send();
}

function displayTable() {

    //Passing a function to getData to be executed upon data reception
    getData(function(data){

        //Code to generate the table using the received data
        //"data" variable here holds the JSON response
        
    });
}

Answer 4

When making AJAX requests, it is important to remember that they are asynchronous processes. They can arrive at any time during execution and JavaScript does not wait for the server response before moving on to the next task. Although there is synchronous XHR available, it is generally not recommended as it goes against the core idea of AJAX.

To handle this asynchronous behavior, a common practice is to use a "callback" function. This function is executed at a later time, allowing you to specify when exactly you want it to run. For example, if you need to generate a table after receiving data:

function getData(callback){
    //Setting up AJAX request
    var request = new XMLHttpRequest();

    //Listening for state changes
    request.onreadystatechange = function() {

        //Checking if the request is complete and successful
        if (request.readyState === 4 && request.status === 200) {
        
            //Executing the callback function with the received data
            callback.call(this, request.responseText);
        }
    }
    request.open("GET", "data.json"); //defaults to asynchronous (true)
    request.send();
}

function displayTable() {

    //Passing a function to getData to be executed upon data reception
    getData(function(data){

        //Code to generate the table using the received data
        //"data" variable here holds the JSON response
        
    });
}

Answer 5

Answer №3

After making the ajax call, it is important to encapsulate all subsequent code within the readystatechange function to ensure proper sequential execution.

Note: The explanation by @Dappergoat offers a clearer insight into this concept.

Answer 6

After making the ajax call, it is important to encapsulate all subsequent code within the readystatechange function to ensure proper sequential execution.

Note: The explanation by @Dappergoat offers a clearer insight into this concept.

Running JavaScript code without blocking the main thread

Answer №1

Answer №2

Answer №3

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