discourse/app/assets/javascripts/select-kit/addon/components/single-select.js

import SelectKitComponent from "select-kit/components/select-kit";
import { computed } from "@ember/object";
import { isEmpty } from "@ember/utils";

export default SelectKitComponent.extend({
  pluginApiIdentifiers: ["single-select"],
  layoutName: "select-kit/templates/components/single-select",
  classNames: ["single-select"],
  singleSelect: true,

  selectKitOptions: {
    headerComponent: "select-kit/single-select-header"
  },

  selectedContent: computed("value", "content.[]", function() {
    if (!isEmpty(this.value)) {
      let content;

      const value =
        this.selectKit.options.castInteger && this._isNumeric(this.value)
          ? Number(this.value)
          : this.value;

      if (this.selectKit.valueProperty) {
        content = (this.content || []).findBy(
          this.selectKit.valueProperty,
          value
        );

        return this.selectKit.modifySelection(
          content || this.defaultItem(value, value)
        );
      } else {
        return this.selectKit.modifySelection(
          (this.content || []).filter(c => c === value)
        );
      }
    } else {
      return this.selectKit.noneItem;
    }
  })
});