Use defineProperty() to avoid eval() and new Function() while preserving arity

index.js

@@ -9,6 +9,7 @@
  */
 
 var eventListenerCount = require('./lib/compat').eventListenerCount
+var wrapFunctionInner = require('./lib/compat').wrapFunctionInner
 var relative = require('path').relative
 
 /**
@@ -65,20 +66,6 @@ function convertDataDescriptorToAccessor (obj, prop, message) {
   return descriptor
 }
 
-/**
- * Create arguments string to keep arity.
- */
-
-function createArgumentsString (arity) {
-  var str = ''
-
-  for (var i = 0; i < arity; i++) {
-    str += ', arg' + i
-  }
-
-  return str.substr(2)
-}
-
 /**
  * Create stack string from stack.
  */
@@ -398,21 +385,13 @@ function wrapfunction (fn, message) {
     throw new TypeError('argument fn must be a function')
   }
 
-  var args = createArgumentsString(fn.length)
+  var deprecate = this
   var stack = getStack()
   var site = callSiteLocation(stack[1])
 
   site.name = fn.name
 
-  // eslint-disable-next-line no-new-func
-  var deprecatedfn = new Function('fn', 'log', 'deprecate', 'message', 'site',
-    '"use strict"\n' +
-    'return function (' + args + ') {' +
-    'log.call(deprecate, message, site)\n' +
-    'return fn.apply(this, arguments)\n' +
-    '}')(fn, log, this, message, site)
-
-  return deprecatedfn
+  return wrapFunctionInner(fn, log, deprecate, message, site)
 }
 
 /**

lib/compat/index.js

@@ -22,6 +22,10 @@ lazyProperty(module.exports, 'eventListenerCount', function eventListenerCount (
   return EventEmitter.listenerCount || require('./event-listener-count')
 })
 
+lazyProperty(module.exports, 'wrapFunctionInner', function wrapFunctionInner () {
+  return require('./wrap-function-inner')
+})
+
 /**
  * Define a lazy property.
  */

lib/compat/wrap-function-inner.js

@@ -0,0 +1,72 @@
+/*!
+ * depd
+ * Copyright(c) 2014-2018 Douglas Christopher Wilson
+ * MIT Licensed
+ */
+
+'use strict'
+
+function canUseDefinePropertyOnFunctionLength () {
+  function detectfn () {}
+
+  try {
+    // Node.js 3.3+.
+    Object.defineProperty(detectfn, 'length', {
+      configurable: true,
+      enumerable: false,
+      value: 1,
+      writable: false
+    })
+  } catch (err) {
+    // Likely Node.js 2.5 or older.
+  }
+
+  return detectfn.length === 1
+}
+
+/**
+ * Create arguments string to keep arity.
+ */
+
+function createArgumentsString (arity) {
+  var str = ''
+
+  for (var i = 0; i < arity; i++) {
+    str += ', arg' + i
+  }
+
+  return str.substr(2)
+}
+
+function wrapFunctionWithDefineProperty (fn, log, deprecate, message, site) {
+  var deprecatedfn = function () {
+    log.call(deprecate, message, site)
+    return fn.apply(this, arguments)
+  }
+
+  // Preserve fn's arity.
+  Object.defineProperty(deprecatedfn, 'length', {
+    configurable: true,
+    enumerable: false,
+    value: fn.length,
+    writable: false
+  })
+
+  return deprecatedfn
+}
+
+function wrapFunctionWithEval (fn, log, deprecate, message, site) {
+  // Preserve fn's arity by manually constructing an arguments string and
+  // eval'ing it into a new function.
+  var args = createArgumentsString(fn.length)
+  // eslint-disable-next-line no-new-func
+  return new Function('fn', 'log', 'deprecate', 'message', 'site',
+    '"use strict"\n' +
+    'return function (' + args + ') {' +
+    'log.call(deprecate, message, site)\n' +
+    'return fn.apply(this, arguments)\n' +
+    '}')(fn, log, deprecate, message, site)
+}
+
+module.exports = canUseDefinePropertyOnFunctionLength()
+    ? wrapFunctionWithDefineProperty : wrapFunctionWithEval