GiavaScript JavaScript Feature Reference

July 3, 2026 · View on GitHub

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Source files:

reference/Language.md
reference/Types.md
reference/Math.md
reference/JSON.md

Language Features

Status of core JavaScript language features in GiavaScript.

Declarations and assignments

Feature	Status
`var` declaration	Available
`var` without initializer	Available
Reassignment with `=`	Available
Compound assignment (`+=`, `-=`, `*=`, `/=`)	Available
Postfix increment and decrement (`++`, `--`)	Available
`import "file.js"`	Available
`let`	Not available
`const`	Not available

Expressions and operators

Feature	Status
Numeric literals (`int`, `float`)	Available
String literals (single and double quotes)	Available
Arithmetic (`+`, `-`, `*`, `/`, `%`)	Available
Exponent operator (`^`, non-standard)	Available
Parenthesized expressions	Available
Comparisons (`<`, `>`, `<=`, `>=`)	Available
Equality (`==`, `!=`)	Available
Strict equality (`===`, `!==`)	Available
Logical operators (`&&`, `\|\|`, `!`)	Available
`typeof` operator	Available
`void` operator	Available
Unary plus (`+`)	Available
Comments (`//`, `/* */`)	Available
Template literals	Available

Equality operator semantics

== and != use coercive (loose) equality behavior.
=== and !== use strict (non-coercive) equality behavior.

`typeof` semantics

typeof returns string representations of value types:

"number" for Int32 and Float64
"string" for String
"boolean" for Bool
"object" for Array, Hash, and null
"function" for callable values (user-defined and built-in)
"undefined" for undefined and undeclared identifiers (does not throw)

Logical operator semantics

a && b: evaluates a first; if a is falsy, returns a and does not evaluate b; otherwise evaluates and returns b.
a || b: evaluates a first; if a is truthy, returns a and does not evaluate b; otherwise evaluates and returns b.
!a: evaluates a and returns a boolean negation (true/false).
a ? b : c: evaluates a first; if a is truthy, evaluates and returns b; otherwise evaluates and returns c.
Precedence: ! binds tighter than &&, && binds tighter than ||, and || binds tighter than ? :.

Spread and rest parameter semantics

Rest parameter (...name) must be the last formal parameter; otherwise an error is raised.
Rest parameters are supported in function declarations, function expressions, and arrow functions.
Rest parameter gathers exceeding arguments into an array. If there are no exceeding arguments, the rest array is empty ([]).
Spread in arrays ([...arr]) creates a shallow copy by iterating elements into a new array. Non-array spread values are silently ignored.
Spread in objects ({...obj}) copies own properties into a new object. Later keys override earlier ones. Non-object spread values are silently ignored.
Spread in function call arguments (fn(...arr)) expands an array into individual arguments. Non-array spread values are silently ignored.
Duplicate parameter names (including rest) are rejected.

Functions and control flow

Feature	Status
Function declarations (`function name(...) { ... }`)	Available
Function expressions (`var f = function(...) { ... }`)	Available
Named function expressions (`var f = function name(...) { ... }`)	Available
Arrow functions (`() => expr`, `x => expr`, `() => { ... }`)	Available
Function calls	Available
Spread in call arguments (`fn(...arr)`)	Available
Rest parameters (`function f(a, ...rest)`, arrow functions)	Available
Returning values with `return`	Available
First-class function values	Available
`if`, `else if`, `else`	Available
C-style `for` loops (`for (init; condition; update)`)	Available
`for...of` loops (iterate over arrays and strings)	Available
`for...in` loops (iterate over object keys)	Available
`break` / `continue` inside loops	Available
`while` / `do...while` loops	Available
Ternary operator (`a ? b : c`)	Available
`switch` statements	Available
`throw` statements	Available
`try` / `catch` / `finally`	Available

Values and collections

Feature	Status
`null`	Available
`undefined`	Available
Array literals and indexing	Available
Spread in arrays (`[...arr]`)	Available
Object literals	Available
Spread in objects (`{...obj}`)	Available
Dot and bracket property access	Available
Template literals	Available

Classic global functions

Feature	Status
`parseInt()`	Available
`parseFloat()`	Available
`isNaN()`	Available
`readLine()`	Available
`Date.now()`	Available
`new Date()`	Available
`console.log()`	Available
`console.warn()`	Available
`console.error()`	Available
`File.read()`	Available
`File.readLines()`	Available
`File.write()`	Available
`File.append()`	Available

Notes

This reflects the current behavior in the interpreter and specs.
let and const declarations return explicit errors: Error: unsupported declaration 'let' and Error: unsupported declaration 'const'.
Use var for variable declarations.
Statements can be separated by newlines without requiring semicolons. A semicolon is not required when two statements are on separate lines.

Type Methods and Properties

Status of built-in methods and properties on GiavaScript runtime types.

String

Member	Kind	Status
`length`	Instance property	Available
`at()`	Instance method	Available
`charAt()`	Instance method	Available
`charCodeAt()`	Instance method	Available
`codePointAt()`	Instance method	Available
`concat()`	Instance method	Available
`endsWith()`	Instance method	Available
`fromCharCode()`	Static method	Available
`includes()`	Instance method	Available
`indexOf()`	Instance method	Available
`isWellFormed()`	Instance method	Available
`lastIndexOf()`	Instance method	Available
`localeCompare()`	Instance method	Available
`match()`	Instance method	Available
`matchAll()`	Instance method	Available
`padEnd()`	Instance method	Available
`padStart()`	Instance method	Available
`repeat()`	Instance method	Available
`replace()`	Instance method	Available
`replaceAll()`	Instance method	Available
`search()`	Instance method	Available
`slice()`	Instance method	Available
`split()`	Instance method	Available
`startsWith()`	Instance method	Available
`substr()`	Instance method	Not available
`substring()`	Instance method	Available
`toLocaleLowerCase()`	Instance method	Available
`toLocaleUpperCase()`	Instance method	Available
`toLowerCase()`	Instance method	Available
`toString()`	Instance method	Available
`toUpperCase()`	Instance method	Available
`toWellFormed()`	Instance method	Available
`trim()`	Instance method	Available
`trimEnd()`	Instance method	Available
`trimStart()`	Instance method	Available
`valueOf()`	Instance method	Available

Number

Member	Kind	Status
`isFinite()`	Static method	Available
`isInteger()`	Static method	Available
`isNaN()`	Static method	Available
`toString()`	Instance method	Available

Array

Member	Kind	Status
`from()`	Static method	Available
`fromAsync()`	Static method	Not available
`isArray()`	Static method	Available
`of()`	Static method	Available
`length`	Instance property	Available
`at()`	Instance method	Available
`concat()`	Instance method	Available
`copyWithin()`	Instance method	Available
`entries()`	Instance method	Available
`every()`	Instance method	Available
`fill()`	Instance method	Available
`filter()`	Instance method	Available
`find()`	Instance method	Available
`findIndex()`	Instance method	Available
`findLast()`	Instance method	Available
`findLastIndex()`	Instance method	Available
`flat()`	Instance method	Available
`flatMap()`	Instance method	Available
`forEach()`	Instance method	Available
`includes()`	Instance method	Available
`indexOf()`	Instance method	Available
`join()`	Instance method	Available
`keys()`	Instance method	Available
`lastIndexOf()`	Instance method	Available
`map()`	Instance method	Available
`pop()`	Instance method	Available
`push()`	Instance method	Available
`reduce()`	Instance method	Available
`reduceRight()`	Instance method	Available
`reverse()`	Instance method	Available
`shift()`	Instance method	Available
`slice()`	Instance method	Available
`some()`	Instance method	Available
`sort()`	Instance method	Available
`splice()`	Instance method	Available
`toLocaleString()`	Instance method	Not available
`toReversed()`	Instance method	Not available
`toSorted()`	Instance method	Not available
`toSpliced()`	Instance method	Not available
`toString()`	Instance method	Available
`unshift()`	Instance method	Available
`values()`	Instance method	Available
`with()`	Instance method	Not available

Array callback argument behavior

In array methods that accept callbacks, JavaScript-compatible argument normalization applies to user-defined function expressions and references to function declarations.
Extra callback arguments are ignored.
Missing callback arguments are passed as undefined.

Object

Member	Kind	Status
`assign()`	Static method	Available
`entries()`	Static method	Available
`hasOwn()`	Static method	Available
`keys()`	Static method	Available
`toString()`	Instance method	Available
`values()`	Static method	Available

Boolean

Member	Kind	Status
`toString()`	Instance method	Available

Date

Member	Kind	Status
`getTime()`	Instance method	Available
`toString()`	Instance method	Available

Date notes

In Node.js, Date.prototype.toString() usually prints a locale/timezone representation.
In GiavaScript, Date.prototype.toString() returns a UTC ISO-like string (YYYY-MM-DDTHH:mm:ss.SSSZ) by design.

Error

Member	Kind	Status
`Error()`	Constructor	Available
`message`	Instance property	Available
`name`	Instance property	Available
`stack`	Instance property	Available
`toString()`	Instance method	Available
`TypeError()`	Constructor	Available
`ReferenceError()`	Constructor	Available
`SyntaxError()`	Constructor	Available

Error notes

new Error("message") creates an error object with the given message.
name defaults to "Error". Subtypes use their constructor name.
stack returns a string representation of the call stack.
toString() returns "name: message".
Error objects can be thrown with throw and caught with try/catch.
Raw value throws continue to work alongside Error objects.

Notes

This reflects the current behavior in the interpreter and specs.

Math

Status of the JavaScript Math global object in GiavaScript.

Member	Kind	Status
`E`	Static property	Available
`LN10`	Static property	Available
`LN2`	Static property	Available
`LOG10E`	Static property	Available
`LOG2E`	Static property	Available
`PI`	Static property	Available
`SQRT1_2`	Static property	Available
`SQRT2`	Static property	Available
`abs()`	Static method	Available
`sqrt()`	Static method	Available
`acos()`	Static method	Available
`acosh()`	Static method	Available
`asin()`	Static method	Available
`asinh()`	Static method	Available
`atan()`	Static method	Available
`atan2()`	Static method	Available
`atanh()`	Static method	Available
`cbrt()`	Static method	Available
`ceil()`	Static method	Available
`clz32()`	Static method	Available
`cos()`	Static method	Available
`cosh()`	Static method	Available
`exp()`	Static method	Available
`expm1()`	Static method	Available
`f16round()`	Static method	Available
`floor()`	Static method	Available
`fround()`	Static method	Available
`hypot()`	Static method	Available
`imul()`	Static method	Available
`log()`	Static method	Available
`log10()`	Static method	Available
`log1p()`	Static method	Available
`log2()`	Static method	Available
`max()`	Static method	Available
`min()`	Static method	Available
`pow()`	Static method	Available
`random()`	Static method	Available
`round()`	Static method	Available
`sign()`	Static method	Available
`sin()`	Static method	Available
`sinh()`	Static method	Available
`sumPrecise()`	Static method	Available
`tan()`	Static method	Available
`tanh()`	Static method	Available
`trunc()`	Static method	Available

Notes

Math.random() returns a pseudo-random number in the range [0, 1).
Math.random() is not cryptographically secure.
Math.max() with zero arguments returns -Infinity. Math.min() with zero arguments returns Infinity.
All Math methods that accept numeric arguments coerce non-numeric values to numbers. Invalid coercions produce NaN or Infinity as appropriate.

JSON

Status of the JavaScript JSON global object in GiavaScript.

Static methods

Member	Kind	Status
`parse()`	Static method	Available
`stringify()`	Static method	Available

Notes

JSON is exposed as a global object.
JSON.parse(string) requires exactly one string argument.
JSON.parse(string) returns runtime values (object, array, number, boolean, null, or string).
JSON.stringify(value) requires exactly one argument.
JSON.stringify(undefined) and JSON.stringify(function) return undefined.
In objects, undefined and function values are omitted.
In arrays, undefined and function values serialize as null.
Non-finite numbers (NaN, Infinity, -Infinity) serialize as null.
Circular arrays and objects raise an error.