eslint-plugin-no-iife

An eslint plugin to prevent immediately-invoked function expression (IIFE) usage in your code.

Installation

npm install --save-dev eslint-plugin-no-iife

Usage

In your .eslintrc (or wherever your eslint configuration lives):

{
  "plugins": [
    "no-iife"
  ],
  "rules": {
    "no-iife/no-iife": "error"
  }
}

Rule details

This rule prevents all immediately-invoked function expressions.

Why

Immediately-invoked function expressions are a messy remnant of early Javascript, and their use today only serves to decrease readability. They can and should be entirely replaced with modern syntax.

Historically, the IIFE had two main advantages. First, it served as a shorthand for calling a function which was just defined. While this pattern can lead to convoluted code, there are a handful of legitimate reasons to call code immediately after definition, such as factory functions. However, it is much more human-readable to define a function and then call it in the next statement. Compare this IIFE:

const x = (function() {
  return function() {
    foo();
  }
})();

With this version:

const y = function() {
  return function() {
    foo();
  }
};
const x = y();

The other use-case for IIFEs was much more practical; imposing a limited scope. The problem arises from var, which hoists variables to the top of the function scope. In a top-level script, the function scope is global, making all the variables global. And since var variables can be reassigned with another use of var, it's all too easy to override existing globals. Besides, having so many global variables makes debugging far more difficult.

IIFEs solve this problem by wrapping a script in an anonymous function, limiting the scope to just one page (or less). This was a savior for many common problems, but at the cost of being messy and confusing.

In modern Javascript, however, var is rarely used, and so the problem of global variable pollution has entirely disappeared. By using const and let, there is simply no need for IIFEs anymore.

License

Copyright (c) 2019 Jade Michael Thornton

Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.