JavaScript WTF

gistfile1.txt

function getArgs() {
  return arguments;
}

// Node REPL
> const args = getArgs(1, 2, 3)
undefined
> args
{ '0': 1, '1': 2, '2': 3 }
> const argsLiteral = { '0': 1, '1': 2, '2': 3 }
undefined
> Array.prototype.slice.call(args)
[ 1, 2, 3 ]
> Array.prototype.slice.call(argsLiteral)
[]

// Err ... why?

> Object.keys(args)
[ '0', '1', '2' ]
> Object.keys(argsLiteral)
[ '0', '1', '2' ]
> Object.is(args, argsLiteral)
false
> Object.keys(args).every(function(key, i) { return args[key] === argsLiteral[key]; });
true

// WAT?

> Object.getOwnPropertyNames(args)
[ '0', '1', '2', 'length', 'callee' ]
> Object.getOwnPropertyNames(argsLiteral)
[ '0', '1', '2' ]

// Oh ... let's try to fix it

> argsLiteral.length = Object.keys(argsLiteral).length
3
> Array.prototype.slice.call(args)
[ 1, 2, 3 ]
> Array.prototype.slice.call(argsLiteral)
[ 1, 2, 3 ]

// But ...

> Object.keys(args)
[ '0', '1', '2' ]
> Object.keys(argsLiteral)
[ '0', '1', '2', 'length' ]
> Object.is(args, argsLiteral)
false
> Object.keys(args).every(function(key, i) { return args[key] === argsLiteral[key]; });
true
> Object.keys(argsLiteral).every(function(key, i) { return args[key] === argsLiteral[key]; });
true