The Tor Browser / file revision

 // yield without an operand causes a warning. See bug 885463.

 load(libdir + "asserts.js");

 assertWarning(() => Function("yield"), SyntaxError,

              "yield followed by EOF should cause a warning");

 assertWarning(() => Function("yield;"), SyntaxError,

              "yield followed by semicolon should cause a warning");

 assertWarning(() => Function("yield\n  print('ok');"), SyntaxError,

              "yield followed by newline should cause a warning");

 assertWarning(() => eval("(function () { yield; })"), SyntaxError,

              "yield followed by semicolon in eval code should cause a warning");

 assertWarning(() => eval("(function () { yield })"), SyntaxError,

              "yield followed by } in eval code should cause a warning");

 assertNoWarning(() => Function("yield 0;"),

                 "yield with an operand should be fine");

 assertNoWarning(() => Function("yield 0"),

                 "yield with an operand should be fine, even without a semicolon");

 print("\npassed - all those warnings are normal and there's no real way to suppress them");