Adds a change to handle when it receives stringified json.

src/lib/field-stringifier.ts

@@ -1,10 +1,10 @@
-import {Field} from './record'
+import { Field } from './record'
 
 const DEFAULT_FIELD_DELIMITER = ','
 const VALID_FIELD_DELIMITERS = [DEFAULT_FIELD_DELIMITER, ';']
 
 export abstract class FieldStringifier {
-    constructor(public readonly fieldDelimiter: string) {}
+    constructor(public readonly fieldDelimiter: string) { }
 
     abstract stringify(value?: Field): string
 
@@ -20,13 +20,29 @@ export abstract class FieldStringifier {
 class DefaultFieldStringifier extends FieldStringifier {
     stringify(value?: Field): string {
         if (this.isEmpty(value)) return ''
+
         const str = String(value)
+
+        if (this.isJSON(str)) return str
+
         return this.needsQuote(str) ? this.quoteField(str) : str
     }
 
     private needsQuote(str: string): boolean {
         return str.includes(this.fieldDelimiter) || str.includes('\r') || str.includes('\n') || str.includes('"')
     }
+
+    private isJSON(str: string): boolean {
+        if (typeof str !== 'string') return false;
+        try {
+            const result = JSON.parse(str);
+            const type = Object.prototype.toString.call(result);
+            return type === '[object Object]'
+                || type === '[object Array]';
+        } catch (err) {
+            return false;
+        }
+    }
 }
 
 class ForceQuoteFieldStringifier extends FieldStringifier {
@@ -44,4 +60,4 @@ function _validateFieldDelimiter(delimiter: string): void {
     if (VALID_FIELD_DELIMITERS.indexOf(delimiter) === -1) {
         throw new Error(`Invalid field delimiter \`${delimiter}\` is specified`)
     }
-}
+}

src/test/field-stringifier.test.ts

@@ -1,6 +1,6 @@
-import {resolveDelimiterChar} from './helper/delimiter'
-import {createFieldStringifier} from '../lib/field-stringifier'
-import {strictEqual} from 'assert'
+import { resolveDelimiterChar } from './helper/delimiter'
+import { createFieldStringifier } from '../lib/field-stringifier'
+import { strictEqual } from 'assert'
 
 describe('DefaultFieldStringifier', () => {
 
@@ -85,6 +85,14 @@ describe('DefaultFieldStringifier', () => {
                 strictEqual(stringifier.stringify(obj), 'Name: OBJECT_NAME')
             })
 
+            it('does not change a stringified object', () => {
+                const obj = {
+                    json: JSON.stringify({ "test": { "type1": "apples", "isObject": true } }),
+                    toString: function () { return this.json }
+                }
+                strictEqual(stringifier.stringify(obj), `{"test":{"type1":"apples","isObject":true}}`)
+            })
+
             it(`wraps a toString-ed field value with double quote if the value contains "${delim}"`, () => {
                 const obj = {
                     name: `OBJECT${delim}NAME`,