Collection has not been initialized when called in async function

Question

function populateList(){
    var _clientContext;
    var _web;
    _clientContext = new SP.ClientContext.get_current();
    _web = _clientContext.get_web();
    var listTitle = "Data1";
    var list = _web.get_lists().getByTitle(listTitle);
    var myquery = new SP.CamlQuery();
    myquery.set_viewXml('valid query');
    var allItems = list.getItems(myquery);
    _clientContext.load(allItems);  
    _clientContext.executeQueryAsync(Function.createDelegate(this, this.onQuerySucceeded()), Function.createDelegate(this, this.onQueryFailed));
}

function onQuerySucceeded() {
    var listEnumerator = this.allItems.getEnumerator(); //this craps out
}

I get the error

"Error: The collection has not been initialized. It has not been requested or the request has not been executed. It may need to be explicitly requested."

Answer 1

The problem lies with object scope. Try below

var allItems;
function populateList(){
    var _clientContext;
    var _web;
    _clientContext = new SP.ClientContext.get_current();
    _web = _clientContext.get_web();
    var listTitle = "Data1";
    var list = _web.get_lists().getByTitle(listTitle);
    var myquery = new SP.CamlQuery();
    myquery.set_viewXml('valid query');
    allItems = list.getItems(myquery);
    _clientContext.load(allItems);  
    _clientContext.executeQueryAsync(Function.createDelegate(this, this.onQuerySucceeded), Function.createDelegate(this, this.onQueryFailed));
}

function onQuerySucceeded() {
    var listEnumerator = allItems.getEnumerator(); //this craps out
}

Answer 2

If you do not want to declare allItems variable outside method then the other way would be to declare allItems inside block but with a 'this' keyword

function populateList(){
    var _clientContext;
    var _web;
    _clientContext = new SP.ClientContext.get_current();
    _web = _clientContext.get_web();
    var listTitle = "Data1";
    var list = _web.get_lists().getByTitle(listTitle);
    var myquery = new SP.CamlQuery();
    myquery.set_viewXml('valid query');
    this.allItems = list.getItems(myquery);
    _clientContext.load(this.allItems);  
    _clientContext.executeQueryAsync(Function.createDelegate(this, this.onQuerySucceeded), Function.createDelegate(this, this.onQueryFailed));
}

function onQuerySucceeded() {
    var listEnumerator = allItems.getEnumerator();
}