Address choumx's feedback.

extensions/amp-list/0.1/amp-list.js

@@ -72,6 +72,9 @@ const TAG = 'amp-list';
 const TABBABLE_ELEMENTS_QUERY =
  'button, a[href], input, select, textarea, [tabindex]:not([tabindex="-1"]), audio[controls], video[controls], [contenteditable]:not([contenteditable="false"])';
 
+// Technically the ':' is not considered part of the scheme, but it is useful to include.
+const AMP_STATE_URI_SCHEME = 'amp-state:';
+
 /**
  * @typedef {{
  * data:(?JsonObject|string|undefined|!Array),
@@ -261,10 +264,6 @@ export class AmpList extends AMP.BaseElement {
  this.initializeLoadMoreElements_();
  }
 
- if (this.isAmpStateSrc_()) {
- return this.getAmpStateJson_().then(json => this.renderLocalData_(json));
- }
-
  return this.fetchList_();
  }
 
@@ -348,49 +347,44 @@ export class AmpList extends AMP.BaseElement {
  /**
  * Returns true if element's src points to amp-state.
  *
+ * @param {string} src
  * @return {boolean}
  * @private
  */
- isAmpStateSrc_() {
- const src = this.element.getAttribute('src');
+ isAmpStateSrc_(src) {
  return (
  isExperimentOn(this.win, 'amp-list-init-from-state') &&
  typeof src === 'string' &&
- startsWith(src, 'amp-state:')
+ startsWith(src, AMP_STATE_URI_SCHEME)
  );
  }
 
  /**
  * Returns json pointed at by an amp-state protocol src. For example,
  * src="amp-state:json.path".
  *
- * @return {Promise<!Object|undefined>}
+ * @param {string} src
+ * @return {Promise<!Object>}
  * @private
  */
- getAmpStateJson_() {
- const src = this.element.getAttribute('src');
- const ampStatePath = src.substring('amp-state:'.length);
+ getAmpStateJson_(src) {
+ const ampStatePath = src.substring(AMP_STATE_URI_SCHEME.length);
  return Services.bindForDocOrNull(this.element).then(bind => {
- if (!bind) {
- const errorMsg =
- 'You must include amp-bind in order to use amp-state as an initial source for amp-list.';
- user().error(TAG, errorMsg);
- return Promise.resolve();
- }
+ user().assert(
+ bind,
+ '"amp-state:" URLs require amp-bind to be installed.',
+ this.element
+ );
  return bind.getState(ampStatePath);
  });
  }
 
  /**
- * @param {!Array|!Object|undefined} json
+ * @param {!Array|!Object} json
  * @return {!Promise}
  * @private
  */
  renderLocalData_(json) {
- if (typeof json === 'undefined') {
- return Promise.resolve();
- }
-
  const array = /** @type {!Array} */ (isArray(json) ? json : [json]);
  this.resetIfNecessary_(/* isFetch */ false);
  return this.scheduleRender_(array, /* append */ false);
@@ -404,11 +398,7 @@ export class AmpList extends AMP.BaseElement {
  const src = mutations['src'];
  const state = /** @type {!JsonObject} */ (mutations)['state'];
  if (src !== undefined) {
- if (this.isAmpStateSrc_()) {
- promise = this.getAmpStateJson_().then(json =>
- this.renderLocalData_(json)
- );
- } else if (typeof src === 'object' && src !== null) {
+ if (typeof src === 'object' && src) {
  promise = this.renderLocalData_(src);
  // Remove the 'src' if it was set by a bind-expression.
  this.element.setAttribute('src', '');
@@ -602,7 +592,11 @@ export class AmpList extends AMP.BaseElement {
  }
 
  let fetch;
- if (this.ssrTemplateHelper_.isEnabled()) {
+ if (this.isAmpStateSrc_(elementSrc)) {
+ fetch = this.getAmpStateJson_(elementSrc).then(json =>
+ this.renderLocalData_(json)
+ );
+ } else if (this.ssrTemplateHelper_.isEnabled()) {
  fetch = this.ssrTemplate_(opt_refresh);
  } else {
  fetch = this.prepareAndSendFetch_(opt_refresh).then(data => {

extensions/amp-list/0.1/test/test-amp-list.js

@@ -1232,8 +1232,9 @@ describes.repeated(
  ampStateJson.setAttribute('type', 'application/json');
  ampStateEl.appendChild(ampStateJson);
  doc.body.appendChild(ampStateEl);
- expectAsyncConsoleError('You must include amp-bind');
- await list.layoutCallback();
+ expect(list.layoutCallback()).to.eventually.throw(
+ 'require amp-bind to be installed'
+ );
  });
 
  it('should render a list using local data', async () => {