perf(util): improve isFormDataLike checks

lib/core/util.js

@@ -354,8 +354,23 @@ function ReadableStreamFrom (iterable) {
   )
 }
 
+// The chunk should be a FormData instance and contains
+// all the required methods.
 function isFormDataLike (chunk) {
-  return chunk && chunk.constructor && chunk.constructor.name === 'FormData'
+  return (chunk &&
+    chunk.constructor && chunk.constructor.name === 'FormData' &&
+    typeof chunk === 'object' &&
+      (typeof chunk.append === 'function' &&
+        typeof chunk.delete === 'function' &&
+        typeof chunk.get === 'function' &&
+        typeof chunk.getAll === 'function' &&
+        typeof chunk.has === 'function' &&
+        typeof chunk.set === 'function' &&
+        typeof chunk.entries === 'function' &&
+        typeof chunk.keys === 'function' &&
+        typeof chunk.values === 'function' &&
+        typeof chunk.forEach === 'function')
+  )
 }
 
 const kEnumerableProperty = Object.create(null)

package.json

@@ -79,6 +79,7 @@
     "cronometro": "^1.0.5",
     "delay": "^5.0.0",
     "docsify-cli": "^4.4.3",
+    "form-data": "^4.0.0",
     "formdata-node": "^4.3.1",
     "https-pem": "^3.0.0",
     "husky": "^8.0.1",

test/fetch/formdata.js

@@ -4,6 +4,8 @@ const { test } = require('tap')
 const { FormData, File, Response } = require('../../')
 const { Blob: ThirdPartyBlob } = require('formdata-node')
 const { Blob } = require('buffer')
+const { isFormDataLike } = require('../../lib/core/util')
+const ThirdPartyFormDataInvalid = require('form-data')
 
 test('arg validation', (t) => {
   const form = new FormData()
@@ -285,6 +287,84 @@ test('formData.constructor.name', (t) => {
   t.end()
 })
 
+test('formData should be an instance of FormData', (t) => {
+  t.plan(3)
+
+  t.test('Invalid class FormData', (t) => {
+    class FormData {
+      constructor () {
+        this.data = []
+      }
+
+      append (key, value) {
+        this.data.push([key, value])
+      }
+
+      get (key) {
+        return this.data.find(([k]) => k === key)
+      }
+    }
+
+    const form = new FormData()
+    t.equal(isFormDataLike(form), false)
+    t.end()
+  })
+
+  t.test('Invalid function FormData', (t) => {
+    function FormData () {
+      const data = []
+      return {
+        append (key, value) {
+          data.push([key, value])
+        },
+        get (key) {
+          return data.find(([k]) => k === key)
+        }
+      }
+    }
+
+    const form = new FormData()
+    t.equal(isFormDataLike(form), false)
+    t.end()
+  })
+
+  test('Invalid third-party FormData', (t) => {
+    const form = new ThirdPartyFormDataInvalid()
+    t.equal(isFormDataLike(form), false)
+    t.end()
+  })
+
+  t.test('Valid FormData', (t) => {
+    const form = new FormData()
+    t.equal(isFormDataLike(form), true)
+    t.end()
+  })
+})
+
+test('FormData should be compatible with third-party libraries', (t) => {
+  t.plan(1)
+
+  class FormData {
+    constructor () {
+      this.data = []
+    }
+
+    append () {}
+    delete () {}
+    get () {}
+    getAll () {}
+    has () {}
+    set () {}
+    entries () {}
+    keys () {}
+    values () {}
+    forEach () {}
+  }
+
+  const form = new FormData()
+  t.equal(isFormDataLike(form), true)
+})
+
 test('arguments', (t) => {
   t.equal(FormData.constructor.length, 1)
   t.equal(FormData.prototype.append.length, 2)