To declare custom element properties with lit-element, add a static properties getter to your custom element class:

static get properties(){
  return {
    myString: String,
    myObject: Object

You can supply any of the properties declared in the static properties getter to the element's _render function. Use JavaScript expressions to insert property values into an HTML template:

_render({myString, myObject}){
  return html`
    <p>myObject.prop1: ${myObject.prop1}</p>
    <p>myObject.prop2: ${myObject.prop2}</p>
**You must declare a property in the `properties` getter AND supply the property name to `_render` in order to use the property value in template markup.** If you forget to supply the property name to `_render`, you may see something like the following error message: wzxhzdk:2

lit-element automatically observes all of the properties you declare in the static properties getter, and efficiently renders the changes in DOM.