Typeof !== "undefined" vs. != null

Safety measures for global identifiers

Using typeof for undeclared variables

When dealing with global identifiers, typeof is your safety net. It avoids throwing the ReferenceError party nobody likes. With undefined being a bit of a chameleon in JavaScript (it can be redefined), typeof is your security agent against such identity crises.

if (typeof neverDeclared === 'undefined') {
  // As secure as a bank vault: checking for undeclared variables
}
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Ensuring 'undefined' stays 'undefined'

If JavaScript was a heist movie, undefined would be the diamond everyone tries to replace. Using an Immediately Invoked Function Expression (IIFE) or the void operator ensures undefined remains undefined.

// IIFE example:
(function(undefined) {
  if (myVar === undefined) {
    // Code Jedi move: myVar is not defined
  }
})();

// Void operator example:
if (myVar === void 0) {
  // Mystery solved: myVar is not defined
}


Coding style considerations

Implications on coding style and analysis

Searching for clear signs in the maze that is JavaScript? Clarity and readability are keys to mastering the labyrinth. typeof input !== 'undefined' is captain obvious, a clear and standard method for checking existence. However, null != input might require a map and compass, potentially conflicting with style guidelines.

Keeping JavaScript environment in mind

Sure, you can use the window object instead of those pesky string comparisons. Sounds cooler, right?

if (window.myVariable === undefined) {
  // Mission accomplished! myVariable is undefined or doesn't exist
}


But remember, assuming you are always in a browser environment is like thinking you are always on vacation. Don't forget about server-side JavaScript like Node.js!

Best practices for checking null or undefined

Checking for both undefined and null

Expecting a visit from an elusive variable (think optional function parameters)? null != input is like an alarm system that catches both null and undefined—caught red-handed!

Encapsulate and conquer!

For ultimate protection, encapsulate your variable checks:

function isDefined(value) {
  return value !== void 0 && value !== null;
}

if (isDefined(myVar)) {
  // And that, my friend, is how you catch both null and undefined
}


Choosing the most suitable techniques

Ensuring code maintainability

A titan of strength in the world of coding is resiliency and readability. Forget relying on devious global variables. Stand tall and make code maintainable with typeof and IIFE.

Making the best choice

The best tool for the job depends on the task. typeof for when existence is the question. null != for when you need to catch both null and undefined. Like picking between Batman and Superman, both get the job done, but your context will determine the best choice.