JSONstringify.js - from-scratch implementation of JSON.stringify as a coding exercise ( and for JScript WSH using CSCRIPT.EXE /nologo MyJScript.js )

JSONstringify.js

// JSONstringify.js - from-scratch implementation of JSON.stringify as a coding exercise ( and for JScript WSH using CSCRIPT.EXE /nologo MyJScript.js )

// 525 chars	_=function(a){var b,c=null,d=typeof a,e=/^(undefined|function|bigint|symbol)$/i,f=0,g=[],h=function(a,b){return a==b?a+"":{}.toString.call(a).slice(8,-1)};if(!e.test(d)){if("string"===d)return"\""+a+"\"";if(!a||"object"!==d||"Number"===h(a))return("Number"===h(a)?isFinite(a)?+a:c:a)+"";if("Date"===h(a)&&!isNaN(a))return _(a.toISOString());if("Array"===h(a)){for(b=a.length;f<b;f++)g.push(_(e.test(h(a[f]))?c:a[f]));return"["+g+"]"}for(f in a)a.hasOwnProperty(f)&&!e.test(h(a[f]))&&g.push(_(f)+":"+_(a[f]));return"{"+g+"}"}}
var JSONstringify = function(obj) {
	var NULL = null;
	var type = typeof obj;
	var skip = /^(undefined|function|bigint|symbol)$/i
	var L;
	var key = 0;
	var elements = [];
	var ctor = function(obj, _UNDEF) {
		return obj == _UNDEF ? String(obj) : {}.toString.call(obj).slice(8, -1);
	};

	if( skip.test(type) ) {
		return;
	};

	if(type === 'string') {
		return '"' + obj + '"';
	};

	if(!obj || type !== 'object' || ctor(obj) === "Number") {
		return (
			String(
				ctor(obj) === "Number" ? isFinite(obj) ? +obj : NULL
				: obj
			)
		);
	};

	if(ctor(obj) === "Date" && !isNaN(obj)) {
		return JSONstringify(obj.toISOString());
	};

	if(ctor(obj) === "Array") {
		for(L = obj.length; key < L; key ++) {
			elements.push(
				JSONstringify(
					skip.test( ctor(obj[key]) ) ? NULL : obj[key]
				)
			);	
		};
		return '[' + elements + ']';
	};

	for(key in obj) {
		if( obj.hasOwnProperty(key) && !skip.test( ctor(obj[key]) ) ) {
			elements.push(
				JSONstringify(key) + ":" + JSONstringify(obj[key])
			);
		};
	};
	return "{" + elements + "}";
};



var stringify_compared_to_JSON = function(func) {

	return [
		func( null ), // => 'null'
		func( true ), // => 'true'
		func( false ), // => 'false'
		func( 0.0 ), // => '0'
		func( "0.0" ), // => "'0.0'"
		func( [] ), // => '[]'
		func( {} ), // => '{}'
		func( location ), // => .match(/^(Location )?{.*\bhref:\s*".+}$/) != null , .match(/^{ancestorOrigins: '\[object DOMStringList\]'/) != null
		func( Infinity ), // => 'null'
		func( NaN ), // => 'null'
		func( undefined ), // => undefined
		func(), // => undefined
		func( Date ), // => undefined
		func( new TypeError("xyz") ), // => '{}'
		func( /z/img ), // => '{}'
		func( [ , ] ), // => '[null]'
		func( new Array(3) ) // => '[null,null,null]'


		/// >> comment out this section for JScript...
		, func( new Map( [ ["3", 6.0], [9.0, "8.0"] ] ) ), // => '{}'
		func( new Set( [3, 6.0, "9", Symbol(3)] ) ), // => '{}'
		func( new Set( [ [3, 6] , [9, 12] ] ) ), // => '{}'
		func( new WeakSet( [Symbol(3)] ) ), // => '{}'
		func( new Int8Array(3) ), // => '{"0":0,"1":0,"2":0}'
		func( new Int8Array( [ 3, 6, 9 ] ) ), // => '{"0":3,"1":6,"2":9}'
		func( Symbol(3) ), // => undefined
		func( x=>Symbol( x ) ), // => undefined
		func === JSONstringify ? func( BigInt(3) ) : undefined // => undefined , instead of TypeError: Do not know how to serialize a BigInt


	];

};



/*@cc_on @if(@_jscript) console={log:function(){var b=arguments;b.length&&WScript.Echo([].join.call(b," "))}}; location={href:WScript.ScriptFullName}; @end@*/
// ^ JScript needs these additional 158 char, to add these 2 Objects that exist in web browsers...
// console={log:function(){var a=arguments;a.length&&WScript.Echo([].join.call(a," "))}};
// location={href:WScript.ScriptFullName};
/*@cc_on @if(@_jscript) Date.prototype.toISOString=function(){var a=this,b="Month",c=function(c,d){var e=a["getUTC"+c]()+(c==b&&1)+"";return"0000".substr(0,(d||2)-e.length)+e};return c("FullYear")+"-"+c(b)+"-"+c("Date")+"T"+c("Hours")+":"+c("Minutes")+":"+c("Seconds")+"."+c("Milliseconds",3)+"Z"} @end@*/
// ^ ...plus these additional 305 char, to add Date.toISOString() which exists in modern JS engines / web browsers

var isWeb = Date.now;
if(isWeb)console.clear();

console.log(stringify_compared_to_JSON(JSONstringify));
if(isWeb) {
	console.log(stringify_compared_to_JSON(JSON.stringify));
	console.log(
		"^ ^ same resulting strings?",
		stringify_compared_to_JSON(JSONstringify).join("|") === stringify_compared_to_JSON(JSON.stringify).join("|")
	);
};
// 	mine BEFORE obj.hasOwnProperty(key)	['null', 'true', 'false', '0', '"0.0"', '[]', '{}', '{"ancestorOrigins":{"length":0},"href":"https://gi…dmia/2883e2e8b321cd5cac37","search":"","hash":""}', 'null', 'null', undefined, undefined, undefined, '{}', '{}', '[null]', '[null,null,null]', '{}', '{}', '{}', '{}', '{"0":0,"1":0,"2":0}', '{"0":3,"1":6,"2":9}', undefined, undefined, undefined]
// 	mine AFTER obj.hasOwnProperty(key)	['null', 'true', 'false', '0', '"0.0"', '[]', '{}', '{"ancestorOrigins":{},"href":"https://gi…dmia/2883e2e8b321cd5cac37","search":"","hash":""}', 'null', 'null', undefined, undefined, undefined, '{}', '{}', '[null]', '[null,null,null]', '{}', '{}', '{}', '{}', '{"0":0,"1":0,"2":0}', '{"0":3,"1":6,"2":9}', undefined, undefined, undefined]
// JSON.stringify...					['null', 'true', 'false', '0', '"0.0"', '[]', '{}', '{"ancestorOrigins":{},"href":"https://gi…dmia/2883e2e8b321cd5cac37","search":"","hash":""}', 'null', 'null', undefined, undefined, undefined, '{}', '{}', '[null]', '[null,null,null]', '{}', '{}', '{}', '{}', '{"0":0,"1":0,"2":0}', '{"0":3,"1":6,"2":9}', undefined, undefined, undefined]



// ONE FINAL TEST: test that all these tests test successfully...
// https://github.com/mdn/content/pull/19595
// ...from the custom function type(value) from MDN for "typeof"...
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/typeof#custom_method_that_gets_a_more_specific_type
var values = [
  5,
  -0,
  new Number(5),
  false,
  null,
  undefined,
  {},
  [],
  new Date( "1 March 2001 1:02:03" + (isWeb ? ".456 am" : " am") ),
  /abc/g,
  { constructor: { name: { something: 'terrible' } } }
];



/// >> comment out this section for JScript...
class Person {}
const mixinClass = (C) => class extends C {};
const MixPerson = mixinClass(Person);
values = values.concat([
  5n,	// BigInt
  () => {},
  async () => {},
  function* () {},
  Promise.resolve(),
  new Set(),
  new Map(),
  new WeakMap(),
  class {},
  class Person {},
  MixPerson,
  new MixPerson(),
  ArrayBuffer,
  new ArrayBuffer(16),
  Symbol.iterator,
  [][Symbol.iterator](),
  {
    [Symbol.toPrimitive]() {
      return 'good';
    },
    toString() {
      throw new Error('bad');
    }
  },
]);



var L = values.length;

// to be consistent, skips BigInt for both, because JSON will throw TypeError: Do not know how to serialize a BigInt
var resultMine = Array(L);
for(var i = 0; i < L; i ++) {
	if(typeof values[i] !== 'bigint')resultMine[i] = JSONstringify( values[i] );
};

var resultJSON = Array(L);
if(isWeb)for(var i = 0; i < L; i ++) {
	if(typeof values[i] !== 'bigint')resultJSON[i] = JSON.stringify( values[i] );
};

console.log(resultMine);
if(isWeb) {
	console.log(resultJSON);
	console.log(
		"^ ^ same resulting strings?",
		resultMine.join("|") === resultJSON.join("|")
	);
};