lib: detach counter from gauge

Author: Qard

doc/api/metrics.md

@@ -345,6 +345,16 @@ added: REPLACEME
 
 The underlying metric instance used for reporting.
 
+#### `counter.value`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+* {number}
+
+The current value of the counter.
+
 #### `counter.increment([n[, meta]])`
 
 <!-- YAML
@@ -389,16 +399,6 @@ errorCount.decrement(2, { errorType: 'timeout' }); // Decrement by 2 with metada
 errorCount.decrement({ errorType: 'timeout' });    // Decrement by 1 with metadata
 ```
 
-#### `counter.value`
-
-<!-- YAML
-added: REPLACEME
--->
-
-* {number}
-
-The current value of the counter.
-
 ### Class: `Gauge`
 
 <!-- YAML

lib/metrics.js

@@ -262,7 +262,37 @@ class Gauge {
 /**
  * An increasing or decreasing value.
  */
-class Counter extends Gauge {
+class Counter {
+  #metric;
+  #value;
+
+  /**
+   * @param {Metric} metric The metric to report to.
+   */
+  constructor(metric) {
+    if (!(metric instanceof Metric)) {
+      throw new ERR_INVALID_ARG_TYPE('metric', ['Metric'], metric);
+    }
+    this.#metric = metric;
+    this.#value = 0;
+  }
+
+  /**
+   * The metric to report to.
+   * @property {Metric} metric
+   */
+  get metric() {
+    return this.#metric;
+  }
+
+  /**
+   * The value of the gauge.
+   * @property {number} value
+   */
+  get value() {
+    return this.#value;
+  }
+
   /**
    * Increment the counter. Negative values invert to positive.
    * @param {number} [n] The amount to increment the counter by. Defaults to 1.
@@ -276,7 +306,8 @@ class Counter extends Gauge {
       n = 1;
     }
 
-    this.reset(this.value + n, meta);
+    this.#value += n;
+    this.metric.report(n, meta);
   }
 
   /**
@@ -292,7 +323,8 @@ class Counter extends Gauge {
       n = 1;
     }
 
-    this.reset(this.value + -n, meta);
+    this.#value -= n;
+    this.metric.report(-n, meta);
   }
 }
 

test/parallel/test-metrics-counter.js

@@ -19,9 +19,9 @@ assert.strictEqual(metric.channelName, 'metrics:counter:test');
 
 const messages = [
   [1, { base: 'test' }],
-  [124, { base: 'test', meta: 'extra' }],
-  [123, { base: 'test' }],
-  [0, { base: 'test', meta: 'extra' }],
+  [123, { base: 'test', meta: 'extra' }],
+  [-1, { base: 'test' }],
+  [-123, { base: 'test', meta: 'extra' }],
 ];
 
 subscribe(metric.channelName, common.mustCall((report) => {