Merge pull request #13905 from Microsoft/optionalParametersInJSFunctions

Treat function paramters in a .js file with no JSDoc as optional

src/compiler/checker.ts

@@ -5241,6 +5241,7 @@ namespace ts {
                 let hasThisParameter: boolean;
                 const iife = getImmediatelyInvokedFunctionExpression(declaration);
                 const isJSConstructSignature = isJSDocConstructSignature(declaration);
+                const isUntypedSignatureInJSFile = !iife && !isJSConstructSignature && isInJavaScriptFile(declaration) && !hasJSDocParameterTags(declaration);
 
                 // If this is a JSDoc construct signature, then skip the first parameter in the
                 // parameter list.  The first parameter represents the return type of the construct
@@ -5269,7 +5270,8 @@ namespace ts {
                     // Record a new minimum argument count if this is not an optional parameter
                     const isOptionalParameter = param.initializer || param.questionToken || param.dotDotDotToken ||
                         iife && parameters.length > iife.arguments.length && !param.type ||
-                        isJSDocOptionalParameter(param);
+                        isJSDocOptionalParameter(param) ||
+                        isUntypedSignatureInJSFile;
                     if (!isOptionalParameter) {
                         minArgumentCount = parameters.length;
                     }

src/compiler/utilities.ts

@@ -1518,6 +1518,11 @@ namespace ts {
         return map(getJSDocs(node), doc => doc.comment);
     }
 
+    export function hasJSDocParameterTags(node: FunctionLikeDeclaration | SignatureDeclaration) {
+        const parameterTags = getJSDocTags(node, SyntaxKind.JSDocParameterTag);
+        return parameterTags && parameterTags.length > 0;
+    }
+
     function getJSDocTags(node: Node, kind: SyntaxKind): JSDocTag[] {
         const docs = getJSDocs(node);
         if (docs) {