Add option to also strip trailing commas (#59)

Co-authored-by: Andrew Bradley <[email protected]>

Author: joshuajaco

index.d.ts

@@ -5,6 +5,13 @@ export interface Options {
 	@default true
 	*/
 	readonly whitespace?: boolean;
+
+	/**
+	Strip trailing commas in addition to comments.
+
+	@default true
+	*/
+	readonly trailingCommas?: boolean;
 }
 
 /**

index.js

@@ -16,7 +16,7 @@ const isEscaped = (jsonString, quotePosition) => {
 	return Boolean(backslashCount % 2);
 };
 
-export default function stripJsonComments(jsonString, {whitespace = true} = {}) {
+export default function stripJsonComments(jsonString, {whitespace = true, trailingCommas = false} = {}) {
 	if (typeof jsonString !== 'string') {
 		throw new TypeError(`Expected argument \`jsonString\` to be a \`string\`, got \`${typeof jsonString}\``);
 	}
@@ -26,13 +26,16 @@ export default function stripJsonComments(jsonString, {whitespace = true} = {})
 	let isInsideString = false;
 	let isInsideComment = false;
 	let offset = 0;
+	let buffer = '';
 	let result = '';
+	let commaIndex = -1;
 
 	for (let index = 0; index < jsonString.length; index++) {
 		const currentCharacter = jsonString[index];
 		const nextCharacter = jsonString[index + 1];
 
 		if (!isInsideComment && currentCharacter === '"') {
+			// Enter or exit string
 			const escaped = isEscaped(jsonString, index);
 			if (!escaped) {
 				isInsideString = !isInsideString;
@@ -44,34 +47,61 @@ export default function stripJsonComments(jsonString, {whitespace = true} = {})
 		}
 
 		if (!isInsideComment && currentCharacter + nextCharacter === '//') {
-			result += jsonString.slice(offset, index);
+			// Enter single-line comment
+			buffer += jsonString.slice(offset, index);
 			offset = index;
 			isInsideComment = singleComment;
 			index++;
 		} else if (isInsideComment === singleComment && currentCharacter + nextCharacter === '\r\n') {
+			// Exit single-line comment via \r\n
 			index++;
 			isInsideComment = false;
-			result += strip(jsonString, offset, index);
+			buffer += strip(jsonString, offset, index);
 			offset = index;
 			continue;
 		} else if (isInsideComment === singleComment && currentCharacter === '\n') {
+			// Exit single-line comment via \n
 			isInsideComment = false;
-			result += strip(jsonString, offset, index);
+			buffer += strip(jsonString, offset, index);
 			offset = index;
 		} else if (!isInsideComment && currentCharacter + nextCharacter === '/*') {
-			result += jsonString.slice(offset, index);
+			// Enter multiline comment
+			buffer += jsonString.slice(offset, index);
 			offset = index;
 			isInsideComment = multiComment;
 			index++;
 			continue;
 		} else if (isInsideComment === multiComment && currentCharacter + nextCharacter === '*/') {
+			// Exit multiline comment
 			index++;
 			isInsideComment = false;
-			result += strip(jsonString, offset, index + 1);
+			buffer += strip(jsonString, offset, index + 1);
 			offset = index + 1;
 			continue;
+		} else if (trailingCommas && !isInsideComment) {
+			if (commaIndex !== -1) {
+				if (currentCharacter === '}' || currentCharacter === ']') {
+					// Strip trailing comma
+					buffer += jsonString.slice(offset, index);
+					result += strip(buffer, 0, 1) + buffer.slice(1);
+					buffer = '';
+					offset = index;
+					commaIndex = -1;
+				} else if (currentCharacter !== ' ' && currentCharacter !== '\t' && currentCharacter !== '\r' && currentCharacter !== '\n') {
+					// Hit non-whitespace following a comma; comma is not trailing
+					buffer += jsonString.slice(offset, index);
+					offset = index;
+					commaIndex = -1;
+				}
+			} else if (currentCharacter === ',') {
+				// Flush buffer prior to this point, and save new comma index
+				result += buffer + jsonString.slice(offset, index);
+				buffer = '';
+				offset = index;
+				commaIndex = index;
+			}
 		}
 	}
 
-	return result + (isInsideComment ? strip(jsonString.slice(offset)) : jsonString.slice(offset));
+	return result + buffer + (isInsideComment ? strip(jsonString.slice(offset)) : jsonString.slice(offset));
 }

index.test-d.ts

@@ -5,3 +5,5 @@ const json = '{/*rainbows*/"unicorn":"cake"}';
 
 expectType<string>(stripJsonComments(json));
 expectType<string>(stripJsonComments(json, {whitespace: true}));
+expectType<string>(stripJsonComments(json, {trailingCommas: true}));
+expectType<string>(stripJsonComments(json, {whitespace: true, trailingCommas: true}));

package.json

@@ -45,5 +45,10 @@
 		"matcha": "^0.7.0",
 		"tsd": "^0.17.0",
 		"xo": "^0.44.0"
+	},
+	"xo": {
+		"rules": {
+			"complexity": "off"
+		}
 	}
 }

readme.md

@@ -49,12 +49,20 @@ Accepts a string with JSON and returns a string without comments.
 
 Type: `object`
 
+
+##### trailingCommas
+
+Type: `boolean`\
+Default: `false`
+
+Strip trailing commas in addition to comments.
+
 ##### whitespace
 
 Type: `boolean`\
 Default: `true`
 
-Replace comments with whitespace instead of stripping them entirely.
+Replace comments and trailing commas with whitespace instead of stripping them entirely.
 
 ## Benchmark
 

test.js

@@ -64,6 +64,16 @@ test('handles weird escaping', t => {
 	t.is(stripJsonComments(String.raw`{"x":"x \"sed -e \\\"s/^.\\\\{46\\\\}T//\\\" -e \\\"s/#033/\\\\x1b/g\\\"\""}`), String.raw`{"x":"x \"sed -e \\\"s/^.\\\\{46\\\\}T//\\\" -e \\\"s/#033/\\\\x1b/g\\\"\""}`);
 });
 
+test('strips trailing commas', t => {
+	t.is(stripJsonComments('{"x":true,}', {trailingCommas: true}), '{"x":true }');
+	t.is(stripJsonComments('{"x":true,}', {trailingCommas: true, whitespace: false}), '{"x":true}');
+	t.is(stripJsonComments('{"x":true,\n  }', {trailingCommas: true}), '{"x":true \n  }');
+	t.is(stripJsonComments('[true, false,]', {trailingCommas: true}), '[true, false ]');
+	t.is(stripJsonComments('[true, false,]', {trailingCommas: true, whitespace: false}), '[true, false]');
+	t.is(stripJsonComments('{\n  "array": [\n    true,\n    false,\n  ],\n}', {trailingCommas: true, whitespace: false}), '{\n  "array": [\n    true,\n    false\n  ]\n}');
+	t.is(stripJsonComments('{\n  "array": [\n    true,\n    false /* comment */ ,\n /*comment*/ ],\n}', {trailingCommas: true, whitespace: false}), '{\n  "array": [\n    true,\n    false  \n  ]\n}');
+});
+
 test.failing('handles malformed block comments', t => {
 	t.is(stripJsonComments('[] */'), '[] */');
 	t.is(stripJsonComments('[] /*'), '[] /*'); // Fails