Why is it possible to call function in JavaScript like this, tested with node.js:
~$ node
> function hi() { console.log("Hello, World!"); };
undefined
> hi
[Function: hi]
> hi()
Hello, World!
undefined
> hi)( // WTF?
Hello, World!
undefined
>
Why does the last call, hi)(
, work? Is it bug in node.js, bug in V8 engine, officially undefined behaviour, or actually valid JavaScript for all interpreters?
It's due to how the REPL evaluates the input, which is ultimately as:
(hi)()
The additional parenthesis are added to force it to be an Expression:
// First we attempt to eval as expression with parens.
// This catches '{a : 1}' properly.
self.eval('(' + evalCmd + ')',
// ...
The intent is to treat {...}
as Object
literals/initialisers rather than as a block.
var stmt = '{ "foo": "bar" }';
var expr = '(' + stmt + ')';
console.log(eval(expr)); // Object {foo: "bar"}
console.log(eval(stmt)); // SyntaxError: Unexpected token :
And, as leesei mentioned, this has been changed for 0.11.x, which will just wrap { ... }
rather than all input:
if (/^\s*\{/.test(evalCmd) && /\}\s*$/.test(evalCmd)) {
// It's confusing for `{ a : 1 }` to be interpreted as a block
// statement rather than an object literal. So, we first try
// to wrap it in parentheses, so that it will be interpreted as
// an expression.
evalCmd = '(' + evalCmd + ')\n';
} else {
// otherwise we just append a \n so that it will be either
// terminated, or continued onto the next expression if it's an
// unexpected end of input.
evalCmd = evalCmd + '\n';
}