feat(adapter): add fetch adapter; (#6371)

lib/utils.js

@@ -209,6 +209,8 @@ const isFormData = (thing) => {
  */
 const isURLSearchParams = kindOfTest('URLSearchParams');
 
+const [isReadableStream, isRequest, isResponse, isHeaders] = ['ReadableStream', 'Request', 'Response', 'Headers'].map(kindOfTest);
+
 /**
  * Trim excess whitespace off the beginning and end of a string
  *
@@ -597,8 +599,7 @@ const toObjectSet = (arrayOrString, delimiter) => {
 const noop = () => {}
 
 const toFiniteNumber = (value, defaultValue) => {
-  value = +value;
-  return Number.isFinite(value) ? value : defaultValue;
+  return value != null && Number.isFinite(value = +value) ? value : defaultValue;
 }
 
 const ALPHA = 'abcdefghijklmnopqrstuvwxyz'
@@ -679,6 +680,10 @@ export default {
   isBoolean,
   isObject,
   isPlainObject,
+  isReadableStream,
+  isRequest,
+  isResponse,
+  isHeaders,
   isUndefined,
   isDate,
   isFile,