Proposal json parse with source

.eslintrc.js

@@ -1,4 +1,8 @@
 module.exports = {
+  parserOptions: {
+    // To support BigInt
+    ecmaVersion: 2020
+  },
   extends: require.resolve('@ostai/eslint-config'),
   rules: {
     'no-underscore-dangle': 0,

README.md

@@ -126,6 +126,7 @@ parse(text, reviver? = null, remove_comments? = false)
 
 - **text** `string` The string to parse as JSON. See the [JSON](http://json.org/) object for a description of JSON syntax.
 - **reviver?** `Function() | null` Default to `null`. It acts the same as the second parameter of [`JSON.parse`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/parse). If a function, prescribes how the value originally produced by parsing is transformed, before being returned.
+  - `comment-json` also passes the 3rd parameter `context` to the function `reviver`, as described in https://github.com/tc39/proposal-json-parse-with-source, which will be useful to parse a JSON string with `BigInt` values.
 - **remove_comments?** `boolean = false` If true, the comments won't be maintained, which is often used when we want to get a clean object.
 
 Returns `CommentJSONValue` (`object | string | number | boolean | null`) corresponding to the given JSON text.
@@ -591,6 +592,12 @@ And it will print:
 }
 ```
 
+## Dealing with `BigInt`s
+
+> Advanced Section
+
+`comment-json` implements the TC39 proposal [proposal-json-parse-with-source](https://github.com/tc39/proposal-json-parse-with-source)
+
 ## License
 
 [MIT](LICENSE)

src/parse.js

@@ -83,9 +83,9 @@ const symbolFor = prefix => Symbol.for(
     : prefix
 )
 
-const transform = (k, v) => reviver
-  ? reviver(k, v)
-  : v
+const transform = (k, {value, context = {}}) => reviver
+  ? reviver(k, value, context)
+  : value
 
 const unexpected = () => {
   const error = new SyntaxError(`Unexpected token '${current.value.slice(0, 1)}', "${current_code}" is not valid JSON`)
@@ -370,12 +370,16 @@ function walk () {
 
   if (tt === CURLY_BRACKET_OPEN) {
     next()
-    return parse_object()
+    return {
+      value: parse_object()
+    }
   }
 
   if (tt === BRACKET_OPEN) {
     next()
-    return parse_array()
+    return {
+      value: parse_array()
+    }
   }
 
   let negative = EMPTY
@@ -388,6 +392,7 @@ function walk () {
   }
 
   let v
+  let source
 
   switch (tt) {
   case 'String':
@@ -396,8 +401,17 @@ function walk () {
   case 'Numeric':
     v = current.value
     next()
-    return JSON.parse(negative + v)
+
+    source = negative + v
+    return {
+      value: JSON.parse(source),
+      context: {
+        source
+      }
+    }
   default:
+    // => unexpected token
+    return {}
   }
 }
 
@@ -423,14 +437,19 @@ const parse = (code, rev, no_comments) => {
 
   parse_comments(PREFIX_BEFORE_ALL)
 
-  let result = walk()
+  const final = walk()
 
   parse_comments(PREFIX_AFTER_ALL)
 
   if (current) {
     unexpected()
   }
 
+  // reviver
+  let result = transform('', final)
+
+  // We should run reviver before the checks below,
+  // otherwise the comment info will be lost
   if (!no_comments && result !== null) {
     if (!isObject(result)) {
       // 1 -> new Number(1)
@@ -446,9 +465,6 @@ const parse = (code, rev, no_comments) => {
 
   restore_comments_host()
 
-  // reviver
-  result = transform('', result)
-
   free()
 
   return result

test/parse.test.js

@@ -312,6 +312,25 @@
       t.is(l.value, 'l')
       t.is(l.inline, false)
     }
+  },
+  {
+    d: 'reviver for BigInt',
+    s: `{
+  // big int
+  "a":9007199254740999
+}`,
+    o: '{"a":9007199254740999}',
+    r: (k, v, {source}) => /^[0-9]+$/.test(source) ? BigInt(source) : v,
+    e (t, obj) {
+      // eslint-disable-next-line
+      t.is(obj.a, 9007199254740999n)
+
+      const [comment] = obj[Symbol.for('before:a')]
+
+      t.is(comment.value, ' big int')
+      t.is(comment.inline, false)
+      t.is(comment.type, 'LineComment')
+    }
   }
 ]
 
@@ -320,12 +339,24 @@
     ? test.only
     : test
 
+  // - d: description
+  // - r: reviver
+  // - s: source
+  // - o: equivalent JSON string of s with comments removed
+  // - e: the expect function to test the result
   tt(c.d, t => {
-    c.e(t, parser.parse(c.s))
+    c.e(
+      t,
+      c.r
+        // reviver
+        ? parser.parse(c.s, c.r)
+        : parser.parse(c.s))
   })
 
   tt(`${c.d}, removes comments`, t => {
-    t.deepEqual(parser.parse(c.s, null, true), parser.parse(c.o))
+    c.r
+      ? t.deepEqual(parser.parse(c.s, c.r, true), parser.parse(c.o, c.r))
+      : t.deepEqual(parser.parse(c.s, null, true), parser.parse(c.o))
   })
 })