perf: remove redundant temporary collections

Direct variable capture measured 91.5 to 71.5 ns for one variable and 2006 to 1544 ns for 20. Swapping drained arrays measured 31.8 to 12.5 ns at one item and 599 to 276 ns at 1000 items on Node 24.18.0 (7 trials, drop best and worst).

Author: BridgeAR

packages/datadog-plugin-child_process/src/scrub-cmd-params.js

@@ -14,18 +14,15 @@ const envVarRegex = new RegExp(ENV_PATTERN)
 const REDACTED = '?'
 
 function extractVarNames (expression) {
-  const varNames = new Set()
+  const varNames = {}
   let match
 
   while ((match = VARNAMES_REGEX.exec(expression))) {
-    varNames.add(match[1])
+    const name = match[1]
+    varNames[name] = `$${name}`
   }
 
-  const varNamesObject = {}
-  for (const varName of varNames) {
-    varNamesObject[varName] = `$${varName}`
-  }
-  return varNamesObject
+  return varNames
 }
 
 function getTokensByExpression (expressionTokens) {

packages/dd-trace/src/exporters/electron/index.js

@@ -16,6 +16,8 @@ class ElectronExporter {
   }
 
   export (spans) {
+    if (!traceChannel.hasSubscribers) return
+
     this.#traces.push(spans)
 
     const { flushInterval } = this._config
@@ -35,9 +37,8 @@ class ElectronExporter {
     clearTimeout(this.#timer)
     this.#timer = undefined
 
-    // eslint-disable-next-line unicorn/prefer-spread -- Avoid invoking a user-overridden array iterator.
-    const traces = this.#traces.slice()
-    this.#traces.length = 0
+    const traces = this.#traces
+    this.#traces = []
 
     if (traces.length > 0 && traceChannel.hasSubscribers) {
       const formattedTraces = traces.map(spans => spans.map(span => normalizeSpan(truncateSpan(span))))

packages/dd-trace/src/opentelemetry/metrics/periodic_metric_reader.js

@@ -253,9 +253,8 @@ class PeriodicMetricReader {
   #collectAndExport (callback = () => {}) {
     // Atomically drain measurements for export. New measurements can be recorded
     // during export without interfering with this batch.
-    // eslint-disable-next-line unicorn/prefer-spread -- Avoid invoking a user-overridden array iterator.
-    const allMeasurements = this.#measurements.slice()
-    this.#measurements.length = 0
+    const allMeasurements = this.#measurements
+    this.#measurements = []
 
     for (const instrument of this.observableInstruments) {
       const observableMeasurements = instrument.collect()

packages/dd-trace/test/exporters/electron/exporter.spec.js

@@ -80,10 +80,11 @@ describe('ElectronExporter', () => {
       sinon.assert.notCalled(traceChannel.publish)
     })
 
-    it('should not publish when there are no subscribers', () => {
+    it('should not buffer when there are no subscribers', () => {
       traceChannel.hasSubscribers = false
 
       exporter.export([span])
+      traceChannel.hasSubscribers = true
       exporter.flush()
 
       sinon.assert.notCalled(traceChannel.publish)