This is a code snippet for the following QlikSense Discussion: https://community.qlik.com/thread/317568

extension.js

//The props get loaded via "define"
return {
    initialProperties: {
        qHyperCubeDef: {
            qDimensions: [],
            qMeasures: [],
            qVariables: [],
            qInitialDataFetch: [{
                qWidth: 10,
                qHeight: 50
            }]
        },
        qVariableListDef: {
            qType: "variable",
            qShowReserved: true,
            qShowConfig: true
        },
        listItems: []
    },
    definition: props,
    support: {
        snapshot: true,
        export: true,
        exportData: true
    },
    paint: function ($element, layout) {
        //My visualisation code
        return qlik.Promise.resolve();
    }
};

properties.js

var appearanceSection = {
    uses: "settings",
    items: {
        colors: colors,
        images: images,
        MyList: {
            type: "array",
            ref: "listItems",
            label: "List Items",
            itemTitleRef: "label",
            allowAdd: true,
            allowRemove: true,
            addTranslation: "Add Item",
            items: {
                button: {
                    label: "Click me",
                    component: "button",
                    action: function (data) {
                        alert("click!");
                    }
                },
                label: {
                    type: "string",
                    ref: "label",
                    label: "Label",
                    expression: "optional"
                },
                textarea: {
                    label: "My textarea",
                    component: "textarea",
                    maxlength: 100,//you shouldn't write too much
                    ref: "myTextarea"
                }
            }
        }
    }
};
// *****************************************************************************
// Main properties panel definition
// Only what is defined here is returned from properties.js
// *****************************************************************************
return {
    type: "items",
    component: "accordion",
    items: {
        dimensions: dimensions,
        measures: measures,
        sorting: sorting,
        appearance: appearanceSection
    }
};