JavaScript Language Support

Literals & types

undefined; null; true; false;
123; 3.14; 0x10;
"abc"; 'xyz';
({a:1, b:2});
[1, 2, 3];

Variables

• let and const (not var)
• Compound assignment: += -= *= /= %= and bitwise variants
• Postfix i++ / i--
• Reassigning const throws assignment to constant

Operators

Arithmetic (+ - * / % **), bitwise, comparison, loose/strict equality, logical, ternary, and typeof.

Control flow

if/else, for, while, do...while, switch, break, continue, try/catch/finally, throw, return.

Functions & closures

• Function declarations and expressions, IIFE
• Arrow functions: x => x*2, (a,b) => a+b, block bodies
• Lexical closures — nested functions capture defining scope
• for (let i = 0; ...) creates a per-iteration binding (loop closure works correctly)

// Closure example
function a() {
  let x = 1;
  function b() {
    let y = 2;
    return function c() { return x + y; };
  }
  return b();
}
a()(); // 3

// Loop closure
let funcs = [];
for (let i = 0; i < 3; i++) {
  funcs[i] = function() { return i; };
}
funcs[0](); // 0

Core built-ins (no extensions)

String methods

length, charCodeAt, charAt, indexOf, substring

Array methods

push, pop, shift, slice, reverse, sort, splice, forEach, map, every, some, find, findIndex, reduce, indexOf, join

Unsupported (current)

Common errors

parse error, ; expected, type mismatch, 'xxx' not found, oom, C stack — most include at line N col M.