console: console.countReset() should emit warning

The Console Standard specifies that console.countReset()
should emit some type of a warning when given a label that
has no previous account associated with it. This PR brings
node's implementation of console.countReset() up-to-spec and
adds a test asserting that a warning is emitted.

Fixes: #20524

PR-URL: #21649
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/console.js

@@ -107,6 +107,7 @@ function Console(options /* or: stdout, stderr, ignoreErrors = true */) {
   if (typeof colorMode !== 'boolean' && colorMode !== 'auto')
     throw new ERR_INVALID_ARG_VALUE('colorMode', colorMode);
 
+  // Corresponds to https://console.spec.whatwg.org/#count-map
   this[kCounts] = new Map();
   this[kColorMode] = colorMode;
 
@@ -308,12 +309,14 @@ Console.prototype.count = function count(label = 'default') {
   this.log(`${label}: ${count}`);
 };
 
-// Not yet defined by the https://console.spec.whatwg.org, but
-// proposed to be added and currently implemented by Edge. Having
-// the ability to reset counters is important to help prevent
-// the counter from being a memory leak.
+// Defined by: https://console.spec.whatwg.org/#countreset
 Console.prototype.countReset = function countReset(label = 'default') {
   const counts = this[kCounts];
+  if (!counts.has(label)) {
+    process.emitWarning(`Count for '${label}' does not exist`);
+    return;
+  }
+
   counts.delete(`${label}`);
 };
 

test/parallel/test-console.js

@@ -35,14 +35,16 @@ if (common.isMainThread) {
 common.expectWarning(
   'Warning',
   [
-    ['No such label \'nolabel\' for console.timeEnd()', common.noWarnCode],
-    ['No such label \'nolabel\' for console.timeLog()', common.noWarnCode],
+    ['Count for \'noLabel\' does not exist', common.noWarnCode],
+    ['No such label \'noLabel\' for console.timeLog()', common.noWarnCode],
+    ['No such label \'noLabel\' for console.timeEnd()', common.noWarnCode],
     ['Label \'test\' already exists for console.time()', common.noWarnCode]
   ]
 );
 
-console.timeEnd('nolabel');
-console.timeLog('nolabel');
+console.countReset('noLabel');
+console.timeLog('noLabel');
+console.timeEnd('noLabel');
 
 console.time('label');
 console.timeEnd('label');
@@ -245,6 +247,6 @@ common.hijackStderr(common.mustCall(function(data) {
 
   // stderr.write will catch sync error, so use `process.nextTick` here
   process.nextTick(function() {
-    assert.strictEqual(data.includes('nolabel'), true);
+    assert.strictEqual(data.includes('noLabel'), true);
   });
 }));