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Defer evaluation on projected arrays #22

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Defer evaluation on projected arrays #22

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44 changes: 27 additions & 17 deletions src/knockout-projections.js
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Original file line number Diff line number Diff line change
Expand Up @@ -244,35 +244,45 @@ See the Apache Version 2.0 License for specific language governing permissions a
var inputObservableArray = this,
arrayOfState = [],
outputArray = [],
outputObservableArray = ko.observableArray(outputArray),
originalInputArrayContents = inputObservableArray.peek();
outputObservableArray = ko.observableArray(outputArray);

// Shorthand syntax - just pass a function instead of an options object
if (typeof mappingOptions === 'function') {
mappingOptions = { mapping: mappingOptions };
}

// Initial state: map each of the inputs
for (var i = 0; i < originalInputArrayContents.length; i++) {
var inputItem = originalInputArrayContents[i],
stateItem = new StateItem(ko, inputItem, i, outputArray.length, mappingOptions, arrayOfState, outputObservableArray),
mappedValue = stateItem.mappedValueComputed.peek();
arrayOfState.push(stateItem);

if (stateItem.isIncluded) {
outputArray.push(mappedValue);
var inputArraySubscription;
function initiateAndSubscribeToChanges() {
// Initial state: map each of the inputs
var originalInputArrayContents = inputObservableArray.peek();
for (var i = 0; i < originalInputArrayContents.length; i++) {
var inputItem = originalInputArrayContents[i],
stateItem = new StateItem(ko, inputItem, i, outputArray.length, mappingOptions, arrayOfState, outputObservableArray),
mappedValue = stateItem.mappedValueComputed.peek();
arrayOfState.push(stateItem);

if (stateItem.isIncluded) {
outputArray.push(mappedValue);
}
}
// If the input array changes structurally (items added or removed), update the outputs
inputArraySubscription = respondToArrayStructuralChanges(ko, inputObservableArray, arrayOfState, outputArray, outputObservableArray, mappingOptions);
}

// If the input array changes structurally (items added or removed), update the outputs
var inputArraySubscription = respondToArrayStructuralChanges(ko, inputObservableArray, arrayOfState, outputArray, outputObservableArray, mappingOptions);

// Return value is a readonly computed which can track its own changes to permit chaining.
// When disposed, it cleans up everything it created.
var returnValue = ko.computed(outputObservableArray).extend({ trackArrayChanges: true }),
var returnValue = ko.computed({ read: function() {
if(!inputArraySubscription) {
initiateAndSubscribeToChanges();
}

return outputObservableArray();
}, deferEvaluation: true }).extend({ trackArrayChanges: true }),
originalDispose = returnValue.dispose;
returnValue.dispose = function() {
inputArraySubscription.dispose();
if(inputArraySubscription) {
inputArraySubscription.dispose();
}
ko.utils.arrayForEach(arrayOfState, function(stateItem) {
stateItem.dispose();
});
Expand Down Expand Up @@ -302,7 +312,7 @@ See the Apache Version 2.0 License for specific language governing permissions a
var projectionFunctionsCacheName = '_ko.projections.cache';

function attachProjectionFunctionsCache(ko) {
// Wraps callback so that, when invoked, its arguments list is prefixed by 'ko' and 'this'
// Wraps callback so that, when invoked, its arguments list is prefixed by 'ko' and 'this'
function makeCaller(ko, callback) {
return function() {
return callback.apply(this, [ko].concat(Array.prototype.slice.call(arguments, 0)));
Expand Down