Bug 1376128 - Use named options for JavaScriptError; r=automatedtester

Using the {foo = null} = {} shorthand to generate default values exposed
as function scope variables is more readable, and arguably somewhat safer,
than the current approach.

MozReview-Commit-ID: Lxn0fpBSR3a

--HG--
extra : rebase_source : 63fa829657d726e8987a77b5add817a3b7d0b7d3

testing/marionette/error.js

@@ -377,20 +377,16 @@ class JavaScriptError extends WebDriverError {
    * @param {string=} script
    *     Script being executed, in text form.
    */
-  constructor (
-      x,
-      fnName = undefined,
-      file = undefined,
-      line = undefined,
-      script = undefined) {
+  constructor(x,
+      {fnName = null, file = null, line = null, script = null} = {}) {
     let msg = String(x);
     let trace = "";
 
-    if (fnName) {
+    if (fnName !== null) {
       trace += fnName;
-      if (file) {
+      if (file !== null) {
         trace += ` @${file}`;
-        if (line) {
+        if (line !== null) {
           trace += `, line ${line}`;
         }
       }
@@ -400,7 +396,7 @@ class JavaScriptError extends WebDriverError {
       let jsStack = x.stack.split("\n");
       let match = jsStack[0].match(/:(\d+):\d+$/);
       let jsLine = match ? parseInt(match[1]) : 0;
-      if (script) {
+      if (script !== null) {
         let src = script.split("\n")[jsLine];
         trace += "\n" +
           `inline javascript, line ${jsLine}\n` +

testing/marionette/evaluate.js

@@ -158,12 +158,12 @@ evaluate.sandbox = function (sb, script, args = [], opts = {}) {
     try {
       res = Cu.evalInSandbox(src, sb, "1.8", opts.filename || "dummy file", 0);
     } catch (e) {
-      let err = new JavaScriptError(
-          e,
-          "execute_script",
-          opts.filename,
-          opts.line,
-          script);
+      let err = new JavaScriptError(e, {
+        fnName: "execute_script",
+        file,
+        line,
+        script,
+      });
       reject(err);
     }