snappymail/vendors/knockout/src/binding/selectExtensions.js

(() => {
    var hasDomDataExpandoProperty = '__ko__hasDomDataOptionValue__';

    // Normally, SELECT elements and their OPTIONs can only take value of type 'string' (because the values
    // are stored on DOM attributes). ko.selectExtensions provides a way for SELECTs/OPTIONs to have values
    // that are arbitrary objects. This is very convenient when implementing things like cascading dropdowns.
    ko.selectExtensions = {
        readValue : element => {
            switch (element.nodeName) {
                case 'OPTION':
                    if (element[hasDomDataExpandoProperty] === true)
                        return ko.utils.domData.get(element, ko.bindingHandlers.options.optionValueDomDataKey);
                    return element.value;
                case 'SELECT':
                    return element.selectedIndex >= 0 ? ko.selectExtensions.readValue(element.options[element.selectedIndex]) : undefined;
                default:
                    return element.value;
            }
        },

        writeValue: (element, value, allowUnset) => {
            switch (element.nodeName) {
                case 'OPTION':
                    if (typeof value === "string") {
                        ko.utils.domData.set(element, ko.bindingHandlers.options.optionValueDomDataKey, undefined);
                        delete element[hasDomDataExpandoProperty];
                        element.value = value;
                    }
                    else {
                        // Store arbitrary object using DomData
                        ko.utils.domData.set(element, ko.bindingHandlers.options.optionValueDomDataKey, value);
                        element[hasDomDataExpandoProperty] = true;

                        // Special treatment of numbers is just for backward compatibility. KO 1.2.1 wrote numerical values to element.value.
                        element.value = typeof value === "number" ? value : "";
                    }
                    break;
                case 'SELECT':
                    // A blank string or null value will select the caption
                    var selection = -1, noValue = ("" === value || null == value);
                    for (var i = 0, n = element.options.length, optionValue; i < n; ++i) {
                        optionValue = ko.selectExtensions.readValue(element.options[i]);
                        // Include special check to handle selecting a caption with a blank string value
                        if (optionValue == value || (optionValue === "" && noValue)) {
                            selection = i;
                            break;
                        }
                    }
                    if (allowUnset || selection >= 0 || (noValue && element.size > 1)) {
                        element.selectedIndex = selection;
                    }
                    break;
                default:
                    element.value = (value == null) ? "" : value;
                    break;
            }
        }
    };
})();