IIFEs (Immediately Invoked Function Expressions) were a key JavaScript pattern before modern language features existed. This post explains what IIFEs are, why they were used for scoping and aliasing in the absence of block scope, and how ES6+ features like `let`/`const`, modules, and top-level `await` have largely made them obsolete. It also covers the nuances of function statements in sloppy vs strict mode, and previews the stage-1 `do` expressions proposal as a cleaner alternative for inline value computation.
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