Usando Knockout js com checkboxes

index.html

<ul data-bind="template: { name: 'choiceTmpl', foreach: choices, templateOptions: { selections: selectedChoices } }"></ul>

<script id="choiceTmpl" type="text/html">
    <li>
        <input type="checkbox" data-bind="attr: { value: $data.id }, checked: $item.selections" />
        <span data-bind="text: $data.descricao"></span>
    </li>
</script>

<hr />

<div data-bind="text: ko.toJSON(selectedChoices)"></div>

<hr />

<div data-bind="text: selectedChoicesDelimited"></div>

script.js

var viewModel = {
    choices: [{id:1,descricao:"Leitura"},{id:2,descricao:"Escrita"},{id:3,descricao:"Gravação"}],
    selectedChoices: ko.observableArray(["2"])
};

viewModel.selectedChoicesDelimited = ko.dependentObservable(function() {
    return this.selectedChoices().join(",");
}, viewModel);

ko.applyBindings(viewModel);