tevador / moddable Goto Github PK

Nonstandard rounding is used when converting a number to decimal string.

XS:

./xst -e "print(17876395023154640000/-13528.07885)"
-1321428949473830.3

V8:

node -e "console.log(17876395023154640000/-13528.07885)"
-1321428949473830.2

The correct value is -1321428949473830.25 and should be rounded to -1321428949473830.2 using the standard 'roundTiesToEven' mode.

XS and V8 differ in the way how they treat invalid assignments.

Examples:

xst -e "function f() { print('Function f called'); } f()=2;"
ReferenceError: no reference

node -e "function f() { console.log('Function f called'); } f()=2;"
Function f called

ReferenceError: Invalid left-hand side in assignment

Here we try to assign a value to a function call. This throws a ReferenceError because the left hand side is not a variable. However, the V8 throws this error after the function is called, while the XS never calls the function.

Same behavior is observed when calling a tagged template.

This may be a violation of the ES6 specification by the V8.

Debug and release builds on raspberry pi (ARMv7 Processor rev 4 (v7l), BCM2835) give:

gdb --args ./xst asdf
...
Program received signal SIGSEGV, Segmentation fault.
0x0001f778 in AllocateNewChunks (index=2)
    at /home/pi/moddable/xs/sources/xsAllocator.c:74
74			((struct SChunk*)(ptr + i))->next = (struct SChunk*)(ptr + i + chunk_size);
(gdb) up
#1  0x0001f854 in my_malloc (size=4)
    at /home/pi/moddable/xs/sources/xsAllocator.c:94
94			chunk = AllocateNewChunks(index);
(gdb) 
#2  0x0001f9f0 in my_calloc (num=4, size=4)
    at /home/pi/moddable/xs/sources/xsAllocator.c:143
143		void* ptr = my_malloc(size);
(gdb) 
#3  0x0003b828 in fxInitializeSharedCluster ()
    at /home/pi/moddable/xs/sources/xsAtomics.c:515
515		gxSharedCluster = c_calloc(sizeof(txSharedCluster), 1);
(gdb) 
#4  0x00116b38 in main (argc=2, argv=0x7efff004)
    at /home/pi/moddable/xs/tools/xst.c:218
218		fxInitializeSharedCluster();

Is this a real bug or am I just using it wrong?

xst -e "let a = 0; try{a++ - /+e++/;}catch(e){print(e);} print(a);"
SyntaxError: invalid regular expression: invalid regular expression:
0

node -e "let a = 0; try{a++ - /+e++/;}catch(e){console.log(e);} console.log(a);"
SyntaxError: Invalid regular expression: /+e++/: Nothing to repeat
1

Here we try to subtract invalid regular expression from a++. The XS fails with an early SyntaxError without executing the code withing the try block. The V8 however evaluates the a++ expression before throwing the error.

This is a bug in the V8: https://bugs.chromium.org/p/v8/issues/detail?id=896

xst -e "print(JSON.stringify(/aaa/))"
undefined

node -e "console.log(JSON.stringify(/aaa/))"
{}

The output from the V8 is the correct one (RegExp is an object with no enumerable properties).

Specification:

Strict mode eval code cannot instantiate variables or functions in the variable environment of the caller to eval. Instead, a new variable environment is created and that environment is used for declaration binding instantiation for the eval code (18.2.1).

xst -e "'use strict'; eval('e=1'); const e = 0;"
ReferenceError: ?: set e: already initialized

Works with a non-constant variable:

xst -e "'use strict'; eval('e=1'); let e = 0;"

xst -e "let c = eval('c=1'); print(c);"
1

node -e "let c = eval('c=1'); console.log(c);"

ReferenceError: c is not defined

Seems like the Temporal dead zone is not supported inside eval.

Numbers in javascript are floats, but this code produces what appears to be an integer overflow:

./xst -e "let q = 2000000000; print(q); q -= (-2000000000); print(q);"

Expected result:

2000000000
4000000000

Actual result (Windows build):

2000000000
-294967296

Actual result (Linux build):

2000000000
1705032704

Sample code:

let x = {};
x.a = x;

try {
  JSON.stringify(x);
} catch(e) {}

delete x.a;

print('Number of keys: ' + Object.keys(x).length);

JSON.stringify(x); //throws here

It seems like the engine 'remembers' that an object had a circular reference and subsequent calls to JSON.stringify fail even if the object is not circular anymore.

Steps to reproduce:

1. Save the above sample code to file "circular.js".
2. Run ./xst -s circular.js
3. Observe output:

Number of keys: 0
TypeError: JSON.stringify: cyclic value