See https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener Bug 1287706 added support for the 'once' option in addEventListener which works like an removeEventListener executed when the callback gets executed for the first time. Advantage: add + remove in one statement, remove can't get lost Try run: https://treeherder.mozilla.org/#/jobs?repo=try-comm-central&revision=27f431f97226 Yes, I made this patch to get used to this new feature.

Comment on attachment 8787905 [details] [diff] [review] patch, v1 Review of attachment 8787905 [details] [diff] [review]: ----------------------------------------------------------------- ::: mail/base/content/glodaFacetView.js @@ +588,4 @@ > // visible state actually happens. > facetDate.getBoundingClientRect(); > } > let listener = () => { This looks weird to me :) I'm not sure what was saved by omitting 'function' here (not your fault). ::: mail/components/preferences/preferencesTab.js @@ +86,5 @@ > > if ("onLoad" in aArgs) { > aTab.browser.addEventListener("paneload", function _contentTab_onLoad (event) { > aArgs.onLoad(event, aTab.browser); > + }, {capture: true, once: true}); Would it be more readable like this? aTab.browser.addEventListener("paneload", function _contentTab_onLoad (event) { aArgs.onLoad(event, aTab.browser); }, {capture: true, once: true}); ::: mail/test/mozmill/shared-modules/test-window-helpers.js @@ +677,3 @@ > focused = true; > } > + targetWindow.addEventListener("focus", onFocus, {capture: true, once: true}); Would this work as targetWindow.addEventListener("focus", function() { focused = true;}, {capture: true, once: true}); ? Or is that too ugly? :)

Comment on attachment 8787905 [details] [diff] [review] patch, v1 Review of attachment 8787905 [details] [diff] [review]: ----------------------------------------------------------------- Looks ok to me, thx! r=mkmelin (I'd fix aceman's second comment, maybe not the first.)

(In reply to :aceman from comment #2) > Comment on attachment 8787905 [details] [diff] [review] > ::: mail/components/preferences/preferencesTab.js > @@ +86,5 @@ > > > > if ("onLoad" in aArgs) { > > aTab.browser.addEventListener("paneload", function _contentTab_onLoad (event) { > > aArgs.onLoad(event, aTab.browser); > > + }, {capture: true, once: true}); > > Would it be more readable like this? > aTab.browser.addEventListener("paneload", > function _contentTab_onLoad (event) { aArgs.onLoad(event, aTab.browser); }, > {capture: true, once: true}); Done. > ::: mail/test/mozmill/shared-modules/test-window-helpers.js > > + targetWindow.addEventListener("focus", onFocus, {capture: true, once: true}); > > Would this work as targetWindow.addEventListener("focus", function() { > focused = true;}, {capture: true, once: true}); ? > Or is that too ugly? :) Changed it to > targetWindow.addEventListener("focus", () => focused = true, {capture: true, once: true}); https://hg.mozilla.org/comm-central/rev/c5b96634312c9f5dec485fdde01e1d77f1d2b33b