Issue 4993 - Add operator-linebreak rule to our JavaScript style guide

pages/coding-style.html

Index: pages/coding-style.html
diff --git a/pages/coding-style.html b/pages/coding-style.html
index a2791736e26db9a375cbcc7185985d1fa73ebaee..12939b36756e1ac73ae2e101dbbc52b68714b712 100644
--- a/pages/coding-style.html
+++ b/pages/coding-style.html
@@ -25,6 +25,7 @@ title=Coding Style
 <ul>
   <li>{{s15 Follow the Mozilla Coding Style's <a href="https://developer.mozilla.org/en-US/docs/Developer_Guide/Coding_Style#JavaScript_practices">JavaScript practices</a>.}}</li>
   <li>{{javascript-strict Always use <a href="https://developer.mozilla.org/docs/Web/JavaScript/Reference/Strict_mode">strict mode</a>.}}</li>
+  <li>{{javascript-operator-linebreak When splitting overlong expressions into multiple lines the joining binary operators should be left at the end of the line, before the linebreak. This does not apply to member access operators, such as <code><fix>.</fix></code> which should be placed on the following line.}}</li>
   <li>{{javascript-if-else-braces When an <code><fix>if</fix></code> statement, an <code><fix>else</fix></code> statement or a loop spans over more than one line always enclose it with braces.}}</li>
   <li>{{s18 In classes, prefix private functions with a single underscore to make them pseudo-private.}}</li>
   <li>{{javascript-spacing-literals Don't add any spaces immediately after opening, or before closing, an object or array literal.}}</li>