feat: Add an option for ignoring trailing commas in object and arrays

A feature included in the JSON5 support. It was added by integrating the JJU parser (a4a606c).

Author: prantlf

README.md

@@ -15,6 +15,7 @@ This is a fork of the original package with the following enhancements:
 * Walks directories recursively (by Paul Vollmer).
 * Provides 100% compatible interface to the native `JSON.parse` method.
 * Optionally recognizes JavaScript-style comments and single quoted strings.
+* Optionally ignores trailing commas in objects and arrays.
 * Supports [JSON Schema] drafts 04, 06 and 07.
 * Prefers the native JSON parser to gain the [best performance], while showing error messages of the same quality.
 * Implements JavaScript modules using [UMD] to work everywhere.
@@ -79,6 +80,7 @@ By default, `jsonlint` will either report a syntax error with details or pretty-
       -M, --mode                   set other parsing flags according to a format type
       -C, --comments               recognize and ignore JavaScript-style comments
       -S, --single-quoted-strings  support single quotes as string delimiters
+      -T, --trailing-commas'       ignore trailing commas in objects and arrays
       -V, --validate [file]        JSON schema file to use for validation
       -e, --environment [env]      which specification of JSON Schema
                                    the validation file uses
@@ -128,6 +130,7 @@ The `parse` method offers more detailed [error information](#error-handling), th
 | Option                     | Description                 |
 | -------------------------- | --------------------------- |
 | `ignoreComments`           | ignores single-line and multi-line JavaScript-style comments during parsing as another "whitespace" (boolean) |
+| `ignoreTrailingCommas`     | ignores trailing commas in objects and arrays (boolean) |
 | `allowSingleQuotedStrings` | accepts strings delimited by single-quotes too (boolean) |
 | `mode`                     | sets multiple options according to the type of input data (string) |
 
@@ -137,7 +140,7 @@ The `mode` parameter (string) sets parsing options to match a common format of i
 | ------- | --------------------------- |
 | `json`  | complies to the pure standard [JSON] (default if not set) |
 | `cjson` | JSON with comments (sets `ignoreComments`) |
-| `json5` | complies to [JSON5]  (sets `ignoreComments`, `allowSingleQuotedStrings` and other flags) |
+| `json5` | complies to [JSON5]  (sets `ignoreComments`, `allowSingleQuotedStrings`, `ignoreTrailingCommas` and enables other JSON5 features) |
 
 ### Schema Validation
 

lib/cli.js

@@ -24,6 +24,7 @@ var options = require('commander')
   .option('-M, --mode [mode]', 'set other parsing flags according to a format type', 'json')
   .option('-C, --comments', 'recognize and ignore JavaScript-style comments')
   .option('-S, --single-quoted-strings', 'support single quotes as string delimiters')
+  .option('-T, --trailing-commas', 'ignore trailing commas in objects and arrays')
   .option('-V, --validate [file]', 'JSON schema file to use for validation')
   .option('-e, --environment [env]', 'which specification of JSON Schema the validation file uses')
   .option('-q, --quiet', 'do not print the parsed json to stdin')
@@ -54,6 +55,7 @@ function parse (source, file) {
     parserOptions = {
       mode: options.mode,
       ignoreComments: options.comments,
+      ignoreTrailingCommas: options.trailingCommas,
       allowSingleQuotedStrings: options.singleQuotedStrings
     }
     parsed = parser.parse(source, parserOptions)

lib/validator.js

@@ -56,6 +56,7 @@
       schema = jsonlint.parse(schema, {
         mode: options.mode,
         ignoreComments: options.ignoreComments,
+        ignoreTrailingCommas: options.ignoreTrailingCommas,
         allowSingleQuotedStrings: options.allowSingleQuotedStrings
       })
       validate = ajv.compile(schema)

src/configurable-parser.js

@@ -14,6 +14,10 @@ function processOptions (options) {
       changed.ignoreComments = this.ignoreComments
       this.ignoreComments = options.ignoreComments
     }
+    if (options.ignoreTrailingCommas !== undefined) {
+      changed.ignoreTrailingCommas = this.ignoreTrailingCommas
+      this.ignoreTrailingCommas = options.ignoreTrailingCommas
+    }
     if (options.allowSingleQuotedStrings !== undefined) {
       changed.allowSingleQuotedStrings = this.allowSingleQuotedStrings
       this.allowSingleQuotedStrings = options.allowSingleQuotedStrings
@@ -44,7 +48,8 @@ var oldNode = typeof process !== 'undefined' && process.version.startsWith('v4.'
 
 function needsCustomParser () {
   return this.ignoreComments || this.allowSingleQuotedStrings ||
-    this.mode === 'cjson' || this.mode === 'json5' || isSafari || oldNode
+    this.ignoreTrailingCommas || this.mode === 'cjson' || this.mode === 'json5' ||
+    isSafari || oldNode
 }
 
 function getReviver (options) {

src/custom-parser.js

@@ -44,6 +44,7 @@ function parseCustom (input, options) { // eslint-disable-line no-unused-vars
 
   var json5 = options.mode === 'json5'
   var ignoreComments = options.ignoreComments || options.mode === 'cjson' || json5
+  var ignoreTrailingCommas = options.ignoreTrailingCommas || json5
   var allowSingleQuotedStrings = options.allowSingleQuotedStrings || json5
   var reviver = options.reviver
 
@@ -230,7 +231,7 @@ function parseCustom (input, options) { // eslint-disable-line no-unused-vars
 
       var char = input[position++]
       if (char === '}' && key === undefined) {
-        if (!json5 && isNotEmpty) {
+        if (!ignoreTrailingCommas && isNotEmpty) {
           --position
           fail('Trailing comma in object')
         }
@@ -305,7 +306,7 @@ function parseCustom (input, options) { // eslint-disable-line no-unused-vars
           fail('Elisions are not supported')
         }
       } else if (char === ']') {
-        if (!json5 && item === undefined && result.length) {
+        if (!ignoreTrailingCommas && item === undefined && result.length) {
           --position
           fail('Trailing comma in array')
         }

web/jsonlint.html

@@ -96,6 +96,10 @@ <h1>JSON Lint</h1>
             <input type="checkbox" id="comments">
             <label for="comments">Ignore JavaScript-style comments</label>
           </div>
+          <div>
+            <input type="checkbox" id="trailing-commas">
+            <label for="trailing-commas">Ignore trailing commas</label>
+          </div>
           <div>
             <input type="checkbox" id="single-quoted-strings">
             <label for="single-quoted-strings">Recognize single-quoted strings</label>
@@ -139,6 +143,7 @@ <h2>Result</h2>
           var parser = jsonlint.parser
           var parserOptions = {
             ignoreComments: document.getElementById('comments').checked,
+            ignoreTrailingCommas: document.getElementById('trailing-commas').checked,
             allowSingleQuotedStrings: document.getElementById('single-quoted-strings').checked
           }
           var parsed = parser.parse(document.getElementById('data').value, parserOptions)