Peter Kröner

Best of the Worst – the most awful anti-features in JavaScript, ranked!

Did you know one JavaScript feature makes all your code slower, even if you never use it? Let's rank the language's worst anti-features.

Best of the Worst – the most awful anti-features in JavaScript, ranked!
#1about 2 minutes

Ranking the worst features in JavaScript's history

An introduction to JavaScript's most confusing and sometimes useful anti-features, ranked using a classic internet tier list.

#2about 4 minutes

The unexpected behavior of primitive object wrappers

Primitive wrappers like `new Boolean(false)` create objects that are always truthy, leading to confusing behavior in conditional statements.

#3about 5 minutes

Using the function constructor to access the global scope

The `new Function()` constructor always executes in the global scope, providing a reliable way to bypass locally shadowed global variables like `window` or `undefined`.

#4about 2 minutes

How JavaScript's global scope and environment records work

The global scope is a special environment record that uses the `window` object as a backend for storing variables.

#5about 3 minutes

Why the `with` statement slows down all JavaScript code

The `with` statement prevents static analysis of variable locations, forcing JavaScript engines to disable certain optimizations and making all code potentially slower.

#6about 3 minutes

How new keywords are added without breaking old code

JavaScript introduces new syntax like `for...of` by using contextual keywords, which are only treated as keywords in specific positions to maintain backwards compatibility.

#7about 6 minutes

The many pitfalls and traps of using parseInt

`parseInt` has multiple issues, including returning a float and auto-detecting hexadecimal prefixes, which can lead to unexpected bugs.

#8about 1 minute

A rapid review of other strange JavaScript features

A quick look at other historical oddities like `document.all`, `new Array()`, and deprecated string HTML wrapper methods.

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