process: refactor process per thread

• Use the `assert` subsystem instead of mocking it.
• Validate the `prevValue` parameter in the `cpuUsage()` function at
the correct place.
• Use validation methods for consistency.
• Use the logical OR assignment operator (`||=`) where appropriate.
• Use `StringPrototypeReplaceAll()` where appropriate.

lib/internal/process/per_thread.js

@@ -23,6 +23,7 @@ const {
   SetPrototypeValues,
   StringPrototypeEndsWith,
   StringPrototypeReplace,
+  StringPrototypeReplaceAll,
   StringPrototypeSlice,
   StringPrototypeStartsWith,
   Symbol,
@@ -33,27 +34,23 @@ const {
 const {
   errnoException,
   codes: {
-    ERR_ASSERTION,
-    ERR_INVALID_ARG_TYPE,
     ERR_INVALID_ARG_VALUE,
     ERR_OUT_OF_RANGE,
     ERR_UNKNOWN_SIGNAL
   }
 } = require('internal/errors');
 const format = require('internal/util/inspect').format;
 const {
+  isInt32,
   validateArray,
   validateNumber,
   validateObject,
 } = require('internal/validators');
+const assert = require('assert');
 const constants = internalBinding('constants').os.signals;
 
 const kInternal = Symbol('internal properties');
 
-function assert(x, msg) {
-  if (!x) throw new ERR_ASSERTION(msg || 'assertion error');
-}
-
 function getFastAPIs(binding) {
   const {
     hrtime: _hrtime
@@ -120,9 +117,9 @@ function wrapProcessMethods(binding) {
   function cpuUsage(prevValue) {
     // If a previous value was passed in, ensure it has the correct shape.
     if (prevValue) {
-      if (!previousValueIsValid(prevValue.user)) {
-        validateObject(prevValue, 'prevValue');
+      validateObject(prevValue, 'prevValue');
 
+      if (!previousValueIsValid(prevValue.user)) {
         validateNumber(prevValue.user, 'prevValue.user');
         throw new ERR_INVALID_ARG_VALUE.RangeError('prevValue.user',
                                                    prevValue.user);
@@ -192,18 +189,15 @@ function wrapProcessMethods(binding) {
   function kill(pid, sig) {
     let err;
 
-    // eslint-disable-next-line eqeqeq
-    if (pid != (pid | 0)) {
-      throw new ERR_INVALID_ARG_TYPE('pid', 'number', pid);
-    }
+    validateNumber(pid, 'pid');
 
     // Preserve null signal
-    if (sig === (sig | 0)) {
+    if (isInt32(sig)) {
       // XXX(joyeecheung): we have to use process._kill here because
       // it's monkey-patched by tests.
       err = process._kill(pid, sig);
     } else {
-      sig = sig || 'SIGTERM';
+      sig ||= 'SIGTERM';
       if (constants[sig]) {
         err = process._kill(pid, constants[sig]);
       } else {
@@ -251,7 +245,6 @@ function wrapProcessMethods(binding) {
   };
 }
 
-const replaceUnderscoresRegex = /_/g;
 const leadingDashesRegex = /^--?/;
 const trailingValuesRegex = /=.*$/;
 
@@ -333,7 +326,7 @@ function buildAllowedFlags() {
       // on a dummy option set and see whether it rejects the argument or
       // not.
       if (typeof key === 'string') {
-        key = StringPrototypeReplace(key, replaceUnderscoresRegex, '-');
+        key = StringPrototypeReplaceAll(key, '_', '-');
         if (RegExpPrototypeTest(leadingDashesRegex, key)) {
           key = StringPrototypeReplace(key, trailingValuesRegex, '');
           return ArrayPrototypeIncludes(this[kInternal].array, key);