您可以通过设置存储到元素中的helper来实现这一点。
例如

function SomeBindingHelper(element, valueAccessor, allBindings, viewModel, bindingContext) {
    var sharedVariable = "Banana";

    // Call on init.
    this.init = function () {
        console.log("init", sharedVariable);
    }

    // Call on update.
    this.update = function () {
        console.log("update", sharedVariable);
    }
}

ko.bindingHandlers.someBinding = {
    init: function (element, valueAccessor, allBindings, viewModel, bindingContext) {
       var bindingHelper = new SomeBindingHelper(element, valueAccessor, allBindings, viewModel, bindingContext);
       bindingHelper.init();
       ko.utils.domData.set(element, "someBindingHelper", bindingHelper);
    },
    update: function (element, valueAccessor, allBindings, viewModel, bindingContext) {
       var bindingHelper = ko.utils.domData.get(element, "someBindingHelper");
       bindingHelper.update();
    }
}

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可能不是在当时的情况下，但任何人在未来绊倒这一点，我发现下面的代码工程。

ko.bindingHandlers.dateselect = {
    init: function (element) {
        this.sharedVar = true;
        var picker = new Pikaday({
            field: element,
        });
    },
    update: function (element) {
        console.log("sharedvar", this.sharedVar); 
        var current = picker.getDate();

    }
};

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