Get JavaScript content

Making a GET request using pure javascript:

var xhttp = new XMLHttpRequest();
  xhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
      document.getElementById("demo").innerHTML =
      this.responseText;
    }
  };
  xhttp.open("GET", "ajax_info.txt", true);
  xhttp.send();

Example taken from W3schools

You can still use the fetch function as mentioned by Caio Saldanha's response.

Placing a request with the jQuery library:

$.get( "ajax/test.html", function( data ) {
  $( ".result" ).html( data );
  alert( "Load was performed." );
});

Example taken from the jQuery documentation

I do not know if I understood correctly, because I do not know what SPOJ rsrsrs .... But I believe that what you want can be done in the following way:

1 - Implement a function to manipulate the ID padding. This function will fire when the onfocusout event occurs in the input.

2 - When firing, the function fetches the endpoint that serves the content you want.

3 - You get the Response from the GET Request made (by fetch ()) and then put the received information in the fields you decide on.

handleIdSearch(event){
 let valor = event.target.value;
 fetch("http://urlDaApi.com.br?idProduto="+valor).then( function(resposta){
      // Veio um objeto do tipo Response, precisamos transformá-lo em JSON
      // Response.json() retorna outra Promise
      return resposta.json();
   }).then( function(json){
      // Pegue os valores do JSON
      document.getElementById("outroInput").value = json.valorOutroInput;
   }).catch( function(error){
      throw error;
   });
}

document.getElementById("campoIdProduto").addEventListener('focusout', 
// Callback do evento
function(event){
    handleIdSearch(event);
})

You go there!