data-bind cache in Knockout.js

JavaScript performance comparison

Revision 16 of this test case created

Preparation code

<div id="main" style="display: none" data-bind="template: 'repeat'"></div>

<script id="repeat" type="text/html">
    <table>
        <tr data-bind="repeat: { foreach: rows, item: '$row' }">
            <td data-bind="repeat: { foreach: $row().cells, item: '$cell', bind: 'text: \'Cell \' + $cell().id()'}"></td>
        </tr>
    </table>
</script>

<script src="//ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script>
<script src="https://github.com/SteveSanderson/knockout/raw/master/build/output/knockout-latest.debug.js">
</script>
<script type='text/javascript' src="https://raw.github.com/mbest/knockout-repeat/master/knockout-repeat.js"></script>


<script>
function Cell(id) {
    this.id = ko.observable(id);   
}
function Row(id) {
    this.id = ko.observable(id);
    this.cells = ko.observableArray();
}

var viewModel = {
    rows: ko.observableArray()
};

for (var i = 0; i < 1000; i++) {
    var row = new Row(i);
    
    for (var j = 0; j < 2000; j++) {
        row.cells.push(new Cell(i + " - " + j));
    }
    viewModel.rows.push(row);
}

ko.utils.buildEvalFunction = function (expression, scopeLevels) {
        // Build the source for a function that evaluates "expression"
        // For each scope variable, add an extra level of "with" nesting
        // Example result: with(sc[1]) { with(sc[0]) { return (expression) } }
        var functionBody = "return (" + expression + ")";
        for (var i = 0; i < scopeLevels; i++) {
                functionBody = "with(sc[" + i + "]) { " + functionBody + " } ";
        }
        return new Function("sc", functionBody);
};


ko.bindingProvider['instance'].bindingCache = {};
var withoutcache = ko.bindingProvider['instance'].parseBindingsString;
var withcache = function(bindingsString, bindingContext) {
        try {
                var viewModel = bindingContext['$data'];
                var scopes = (typeof viewModel == 'object' && viewModel != null) ? [viewModel, bindingContext] : [bindingContext];
                var cacheKey = scopes.length + '_' + bindingsString;
                var bindingFunction;
                if (cacheKey in this.bindingCache) {
                        bindingFunction = this.bindingCache[cacheKey];
                } else {
                        var rewrittenBindings = " { " + ko.jsonExpressionRewriting.insertPropertyAccessorsIntoJson(bindingsString) + " } ";
                        bindingFunction = this.bindingCache[cacheKey] = ko.utils.buildEvalFunction(rewrittenBindings, scopes.length);
                }
                return bindingFunction(scopes);
        } catch (ex) {
                throw new Error("Unable to parse bindings.\nMessage: " + ex + ";\nBindings value: " + bindingsString);
        }           
};

</script>
<script>
  Benchmark.prototype.setup = function() {
    ko.utils.emptyDomNode($("#main")[0]);
    ko.bindingProvider['instance'].bindingCache = {};
    
  };
</script>

Preparation code output

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Testing in unknown unknown
Test Ops/sec
with cache
 
ko.bindingProvider['instance'].parseBindingsString = withcache;

var main = $("#main");
ko.applyBindings(viewModel, main[0]);
 
 pending…
without cache
 
ko.bindingProvider['instance'].parseBindingsString = withoutcache;

var main = $("#main");
ko.applyBindings(viewModel, main[0]);
 
 pending…

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