factor fetch import into NodeJSLib

javascript/ql/src/semmle/javascript/frameworks/ClientRequests.qll

@@ -267,17 +267,7 @@ module ClientRequest {
     DataFlow::Node url;
 
     FetchUrlRequest() {
-      exists(string moduleName, DataFlow::SourceNode callee | this = callee.getACall() |
-        (
-          moduleName = "node-fetch" or
-          moduleName = "cross-fetch" or
-          moduleName = "isomorphic-fetch"
-        ) and
-        callee = DataFlow::moduleImport(moduleName) and
-        url = getArgument(0)
-      )
-      or
-      this = DataFlow::globalVarRef("fetch").getACall() and
+      this = NodeJSLib::Fetch::moduleImport() and
       url = getArgument(0)
     }
 

javascript/ql/src/semmle/javascript/frameworks/NodeJSLib.qll

@@ -1134,4 +1134,18 @@ module NodeJSLib {
       result = moduleImport().getAPropertyRead(member)
     }
   }
+
+  /**
+   * Provides predicates for working with the "node-fetch" module and its platform-specific instances as a single module.
+   */
+  module Fetch {
+    /**
+     *  Gets a node that imports the "node-fetch" module, or one of its platform-specific instances.
+     */
+    DataFlow::SourceNode moduleImport() {
+      result = DataFlow::moduleImport(["node-fetch", "cross-fetch", "isomorphic-fetch"])
+      or
+      result = DataFlow::globalVarRef("fetch")
+    }
+  }
 }