Javascript function call with/without parentheses

Question

code_0:

(calling foo without parentheses)

function foo(){
    console.log(\'hello world\');
}

setTimeout(foo, 2000);

This

Answer 1

The basic difference between foo and foo() is the following:

function foo() {
   alert("bar");
   return "baz";
}

console.log(foo); // gives "function"
console.log(foo());  // gives "baz"

foo is a reference to the function body itself while foo() executes the function. Thus

setTimeout(foo(), 2000);

passes the return value ("baz") to the function setTimeout(which will result in an error). setTimeout expects an "executable" function as first argument, so you need to pass in a reference to an existing function.