Caching JavaScript promise results

Question

I would make one call to the server to get a list of items. How do I make sure that only one call is made and the collections is processed only once to create a key value ma

Answer 1

I think what you're really looking for is

var cache = null; // cache for the promise
function getItems() {
    return cache || (cache = getAllItemsFromServer().then(function(data){
        var itemMap = {};
        data.forEach(function(value){
            itemMap[value.key] = value;
        });
        return itemMap;
    }));
}

var itemKeys = ['a', 'b', 'c'];
itemKeys.forEach(function(key){
    getItems().then(function(data){
        return data[key];
    }).then(function(value) {
        console.log('item for key=' + value);
    }); // notice that you get the value only asynchronously!
});