Precedence of function object expression in ECMAScript

Question

In order to implement a tiny compiler that emits ECMAScript I need to know how strong a function object expression binds, i.e. what is the precedence of the "operator" function(a1, a2, ...) { ... }?

For example, how is function(a1, a2, ...) { ... } (b1, b2, ...) supposed to be parsed? To get the wished for result, namely the application of b1, b2, ... to the function object, I have to use parentheses around the function object in the Rhino interpreter.

Answer 1

Your function(a1, a2, ...) { ... } (b1, b2, ...) is invalid, and should return a Syntax Error. ECMAScript has the concept of a FunctionDeclaration as well as that of a FunctionExpression. You may want to check out the following:

• Function expressions vs. Function declarations
• Explain JavaScript's encapsulated anonymous function syntax (@CMS' answer)

While a FunctionExpression is an operator, the FunctionDeclaration is a special syntax used for declaring functions, which are automatically hoisted to the top of the enclosing scope.

Wrapping a function in the grouping operator (parenthesis) will force the interpreter to treat it as a FunctionExpression.

If you try the following in Firebug:

function () { alert('test'); }();       // Syntax Error
(function () { alert('test'); })();     // Works fine

Answer 2

To execute a function literal, it needs to be enclosed in parentheses. Either:

(function(...){...})(...);

or:

(function(...){...}(...));

Without the parentheses it produces a syntax error.