Bug 1610754 - Display falsy values in eager evaluation result. r=jlast.

We weren't displaying results when they were
falsy (0, false, empty string, ...). This is
fixed by this patch that adds a few test cases
to ensure we don't regress.

Differential Revision: https://phabricator.services.mozilla.com/D60692

--HG--
extra : moz-landing-system : lando

devtools/client/webconsole/actions/input.js

@@ -265,8 +265,11 @@ function terminalInputChanged(expression) {
 
 function getEagerEvaluationResult(response) {
   const result = response.exception || response.result;
-  // Don't show syntax errors or undefined results to the user.
-  if (!result || result.isSyntaxError || result.type == "undefined") {
+  // Don't show syntax errors results to the user.
+  if (
+    (result && result.isSyntaxError) ||
+    (result && result.type == "undefined")
+  ) {
     return null;
   }
 

devtools/client/webconsole/test/browser/browser_jsterm_eager_evaluation.js

@@ -39,6 +39,18 @@ add_task(async function() {
   setInputValue(hud, "x + y + undefined");
   await waitForEagerEvaluationResult(hud, "NaN");
 
+  setInputValue(hud, "1 - 1");
+  await waitForEagerEvaluationResult(hud, "0");
+
+  setInputValue(hud, "!true");
+  await waitForEagerEvaluationResult(hud, "false");
+
+  setInputValue(hud, `"ab".slice(0, 0)`);
+  await waitForEagerEvaluationResult(hud, `""`);
+
+  setInputValue(hud, `JSON.parse("null")`);
+  await waitForEagerEvaluationResult(hud, "null");
+
   setInputValue(hud, "-x / 0");
   await waitForEagerEvaluationResult(hud, "-Infinity");