JSFiddle - React, Tailwind, and code Playground

JavaScript

var IDs = ["1", "2", "1", "3", "1"];
//ID "1" is repeated
//data for "1" should should require ajax get the first time
//subsequent processing should get data for "1" from dataCache
var dataCache = {};

function getData(ID) {
    if (ID in dataCache) {
        console.log("cache hit for ID " + ID);
        return dataCache[ID];
    } else {
        console.log("retrieving data for ID " + ID);
        return $.getJSON("http://jsfiddle.net/echo/jsonp/?callback=?", {
            id: ID
        }, function(response) {
            console.log("caching data for ID " + ID);
            dataCache[ID] = response;
        });
    }
}

for (var i=0; i<IDs.length; i++) {
    $.when( getData(IDs[i]) ).then( function(result) {
        console.log(result);
    });
}