Object function properties should call next()

Author: blakeembrey

src/function.ts

@@ -1,4 +1,4 @@
-import { Next } from "./types";
+import { Next, ToString } from "./types";
 import { quoteKey, isValidVariableName } from "./quote";
 
 /**
@@ -35,12 +35,22 @@ const TOKENS_PRECEDING_REGEXPS = new Set(
   ).split(" ")
 );
 
+/**
+ * Track function parser usage.
+ */
+export const USED_METHOD_KEY = new WeakSet<Function>();
+
 /**
  * Stringify a function.
  */
-export function functionToString(fn: Function, space: string, next: Next) {
-  return new FunctionParser(fn, space, next).stringify();
-}
+export const functionToString: ToString = (fn, space, next, key) => {
+  const name = typeof key === "string" ? key : undefined;
+
+  // Track in function parser for object stringify to avoid duplicate output.
+  if (name !== undefined) USED_METHOD_KEY.add(fn);
+
+  return new FunctionParser(fn, space, next, name).stringify();
+};
 
 /**
  * Rewrite a stringified function to remove initial indentation.
@@ -78,7 +88,7 @@ export class FunctionParser {
     public fn: Function,
     public indent: string,
     public next: Next,
-    public key?: PropertyKey
+    public key?: string
   ) {
     this.fnString = Function.prototype.toString.call(fn);
     this.fnType = fn.constructor.name as keyof typeof FUNCTION_PREFIXES;

src/index.spec.ts

@@ -857,6 +857,39 @@ describe("javascript-stringify", () => {
 
       expect(result).toEqual("[object Object]");
     });
+
+    it("should support object functions", () => {
+      function makeRaw(str: string) {
+        const fn = () => {
+          /* Noop. */
+        };
+        fn.__expression = str;
+        return fn;
+      }
+
+      const result = stringify(
+        {
+          "no-console": makeRaw(
+            `process.env.NODE_ENV === 'production' ? 'error' : 'off'`
+          ),
+          "no-debugger": makeRaw(
+            `process.env.NODE_ENV === 'production' ? 'error' : 'off'`
+          )
+        },
+        (val, indent, stringify) => {
+          if (val && val.__expression) {
+            return val.__expression;
+          }
+          return stringify(val);
+        },
+        2
+      );
+
+      expect(result).toEqual(`{
+  'no-console': process.env.NODE_ENV === 'production' ? 'error' : 'off',
+  'no-debugger': process.env.NODE_ENV === 'production' ? 'error' : 'off'
+}`);
+    });
   });
 
   describe("max depth", () => {

src/object.ts

@@ -27,25 +27,22 @@ const rawObjectToString: ToString = (obj, indent, next) => {
   const values = Object.keys(obj)
     .reduce(
       function(values, key) {
-        if (typeof obj[key] === "function") {
-          const parser = new FunctionParser(obj[key], indent, next, key);
-          const result = parser.stringify();
-          values.push(indent + result.split("\n").join(`\n${indent}`));
-          return values;
-        }
-
-        const result = next(obj[key], key);
+        const fn = obj[key];
+        const result = next(fn, key);
 
         // Omit `undefined` object entries.
         if (result === undefined) return values;
 
         // String format the value data.
         const value = result.split("\n").join(`\n${indent}`);
 
-        values.push(
-          `${indent}${quoteKey(key, next)}:${indent ? " " : ""}${value}`
-        );
+        // Skip `key` prefix for function parser.
+        if (USED_METHOD_KEY.has(fn)) {
+          values.push(`${indent}${value}`);
+          return values;
+        }
 
+        values.push(`${indent}${quoteKey(key, next)}:${space}${value}`);
         return values;
       },
       [] as string[]