5 | title: JSON.parse source text access 6 | status: proposal 7 | stage: 4 8 | shortname: <a href="https://github.com/tc39/proposal-json-parse-with-source">proposal-json-parse-with-source</a> 9 | contributors: Richard Gibson 10 |11 |
The JSON object:
42 |The JSON Data Interchange Format is defined in ECMA-404. The JSON interchange format used in this specification is exactly that described by ECMA-404. Conforming implementations of `JSON.parse` and `JSON.stringify` must support the exact interchange format described in the ECMA-404 specification without any deletions or extensions to the format.
52 | 53 | 54 |This function performs the following steps when called:
57 |This function parses a JSON text (a JSON-formatted String) and produces an ECMAScript language value. The JSON format represents literals, arrays, and objects with a syntax similar to the syntax for ECMAScript literals, Array Initializers, and Object Initializers. After parsing, JSON objects are realized as ECMAScript objects. JSON arrays are realized as ECMAScript Array instances. JSON strings, numbers, booleans, and null are realized as ECMAScript Strings, Numbers, Booleans, and *null*.
67 |The optional _reviver_ parameter is a function that takes two parameters, _key_ and _value_. It can filter and transform the results. It is called with each of the _key_/_value_ pairs produced by the parse,For each value produced by the parse, it is called with three arguments (the key, the value, and a context object containing [for unmodified primitive values] details of the corresponding Parse Node) and its return value is used instead of the original value. If it returns what it received, the structure is not modified. If it returns *undefined* then the property is deleted from the result.
The *"length"* property of the `parse` function is *2*𝔽.
89 |Valid JSON text is a subset of the ECMAScript |PrimaryExpression| syntax. Step
However, because
A JSON Parse Record is a Record value used to describe the initial state of a value parsed from JSON text.
98 |JSON Parse Records have the fields listed in
| Field Name | 103 |Value | 104 |Meaning | 105 |
|---|---|---|
| [[ParseNode]] | 108 |a Parse Node | 109 |The context Parse Node. | 110 |
| [[Key]] | 113 |a property name | 114 |The property name with which [[Value]] is associated. | 115 |
| [[Value]] | 118 |an ECMAScript language value | 119 |The value produced by evaluation of [[ParseNode]]. | 120 |
| [[Elements]] | 123 |a List of JSON Parse Records | 124 |JSON Parse Records corresponding with the elements of a [[Value]] that is an Array, in order. If [[Value]] is not an Array, the List will be empty. | 125 |
| [[Entries]] | 128 |a List of JSON Parse Records | 129 |JSON Parse Records corresponding with the entries of a [[Value]] that is a non-Array Object, in source order. If [[Value]] is not a non-Array Object, the List will be empty. | 130 |
{"a":"lost","a":"kept"}), the value for the corresponding property of the resulting ECMAScript object is specified by the last pair with that name.
173 | 1. Let _propertyDefinition_ be ~empty~.
174 | 1. For each Parse Node _propertyNode_ of _propertyNodes_, do
175 | 1. Let _propName_ be PropName of _propertyNode_.
176 | 1. If SameValue(_propName_, _P_) is *true*, set _propertyDefinition_ to _propertyNode_.
177 | 1. Assert: _propertyDefinition_ is This algorithm intentionally does not throw an exception if either [[Delete]] or CreateDataProperty return *false*.
201 |It performs the following steps when called:
203 |It is not permitted for a conforming implementation of `JSON.parse` to extend the JSON grammars. If an implementation wishes to support a modified or extended JSON interchange format it must do so by defining a different parse function.
244 |In the case where there are duplicate name Strings within an object, lexically preceding values for the same key shall be overwritten.
246 |number token may represent a negative value. In ECMAScript, negation is represented as a unary operation.
271 | 1. If _type_ is |UnaryExpression|, then
272 | 1. Set _unaryExpression_ to _candidate_.
273 | 1. Else if _type_ is |NumericLiteral|, then
274 | 1. Assert: _candidate_ is contained within _unaryExpression_.
275 | 1. Return _unaryExpression_.
276 | 1. Else,
277 | 1. Return _candidate_.
278 | 1. If _queuedChildren_ is *false* and _candidate_ is an instance of a nonterminal and _candidate_ Contains _type_ is *true*, then
279 | 1. Let _children_ be a List containing each child node of _candidate_, in order.
280 | 1. Set _queue_ to the list-concatenation of _queue_ and _children_.
281 | 1. Set _queuedChildren_ to *true*.
282 | 1. Return ~empty~.
283 | 286 | It may make sense to generalize this operation and define Contains in terms of it rather than vice versa, but Contains is currently limited to a single target nonterminal and has specialized treatment for e.g. |ClassTail| descending into |ClassBody| exclusively to inspect computed names. 287 |
288 |The `rawJSON` function returns an object representing raw JSON text of a string, number, boolean, or null value.
297 |value is an object or array as defined in that specification.
301 | 1. Let _internalSlotsList_ be « [[IsRawJSON]] ».
302 | 1. Let _obj_ be OrdinaryObjectCreate(*null*, _internalSlotsList_).
303 | 1. Perform ! CreateDataPropertyOrThrow(_obj_, *"rawJSON"*, _jsonString_).
304 | 1. Perform ! SetIntegrityLevel(_obj_, ~frozen~).
305 | 1. Return _obj_.
306 | The `stringify` function returns a String in UTF-16 encoded JSON format representing an ECMAScript language value, or *undefined*. It can take three parameters. The _value_ parameter is an ECMAScript language value, which is usually an object or array, although it can also be a String, Boolean, Number or *null*. The optional _replacer_ parameter is either a function that alters the way objects and arrays are stringified, or an array of Strings and Numbers that acts as an inclusion list for selecting the object properties that will be stringified. The optional _space_ parameter is a String or Number that allows the result to have white space injected into it to improve human readability.
313 | 314 |?u/The JSON object:
2558 |parse and stringify,new operator.The JSON Data Interchange Format is defined in ECMA-404. The JSON interchange format used in this specification is exactly that described by ECMA-404. Conforming implementations of JSON.parse and JSON.stringify must support the exact interchange format described in the ECMA-404 specification without any deletions or extensions to the format.
This function performs the following steps when called:
2573 |This function parses a JSON text (a JSON-formatted String) and produces an
The optional reviver parameter is a function that takes two parameters, key and value. It can filter and transform the results. It is called with each of the key/value pairs produced by the parse,For each value produced by the parse, it is called with three arguments (the key, the value, and a context object containing [for unmodified primitive values] details of the corresponding
The parse function is
Valid JSON text is a subset of the ECMAScript
However, because JSON.parse, the same source text can produce different results when evaluated as a JSON.parse, means that not all texts accepted by JSON.parse are valid as a
A JSON Parse Record is a
JSON Parse Records have the fields listed in
| Field Name | 2597 |Value | 2598 |Meaning | 2599 |
|---|---|---|
| [[ParseNode]] | 2602 |a |
2603 | The context |
2604 |
| [[Key]] | 2607 |a |
2608 | The |
2609 |
| [[Value]] | 2612 |an |
2613 | The value produced by evaluation of [[ParseNode]]. | 2614 |
| [[Elements]] | 2617 |a |
2618 | |
| [[Entries]] | 2622 |a |
2623 |
The abstract operation CreateJSONParseRecord takes arguments parseNode (a
{"a":"lost","a":"kept"}), the value for the corresponding property of the resulting ECMAScript object is specified by the last pair with that name.The abstract operation InternalizeJSONProperty takes arguments holder (an Object), name (a String), reviver (a
This algorithm intentionally does not throw an exception if either [[Delete]] or
It performs the following steps when called:
2650 |It is not permitted for a conforming implementation of JSON.parse to extend the JSON grammars. If an implementation wishes to support a modified or extended JSON interchange format it must do so by defining a different parse function.
In the case where there are duplicate name Strings within an object, lexically preceding values for the same key shall be overwritten.
2654 |The
JSON.parse built-in number token may represent a negative value. In ECMAScript, negation is represented as a unary operation.
2664 | It may make sense to generalize this operation and define
The rawJSON function returns an object representing raw JSON text of a string, number, boolean, or null value.
value is an object or array as defined in that specification.The stringify function returns a String in UTF-16 encoded JSON format representing an
The abstract operation SerializeJSONProperty takes arguments state (a
The
The
© 2025 Richard Gibson
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