Final answer:
The given code snippet does not work as an IIFE because it lacks the necessary parentheses to make the function declaration into an executable function expression. An IIFE requires wrapping the entire function in parentheses, followed by another set to invoke it immediately.
Step-by-step explanation:
The reason the code snippet function foo(){ }(); does not work as an Immediately Invoked Function Expression (IIFE) is that the syntax is incorrect for an IIFE.
For a function to be invoked immediately, it must be made into an expression, which can then be executed right away.
This typically involves wrapping the entire function declaration in parentheses to indicate that it is a function expression, followed by another set of parentheses to call the function immediately.
An appropriate IIFE should be structured as (function foo(){ })(); or (function(){ })(); if the function does not need a name.
The additional parentheses around the function turn the function declaration into an expression, which is then executed by the trailing parentheses.