An incomplete list of bizarre failings of the JavaScript programming language

javascript_madness.md

• Prototypal inheritance forces an unstated empty object onto your object with key prototype
• functions can act as object constructors but with the same syntax
• empty array members break loops
• Infinity/-Infinity
• +0/-0
• null is an object
• testing NaN === NaN is always false
• typeof always returns object" for all different reference types
• the type of NaN (not a number) is literally "number" but as a string
• void looks like a Java class but its only job is to return undefined
• undefined is a global var which is different from but has type of undefined
• undefined can also be redefined
• null and undefined both exist
• reference types were made to look like Java and should be avoided but are still force converted on to you under the hood on some objects
• the DOM api in general
• this
• callback hell
• hoisting
• parseInt() defaults to base 2 not base 10
• .sort converts array members to strings making 10 appear before 1
• { } + { } = "" empty string
• 0.1 + 0.2 = 0.30000000000000004
• you can monkey patch/blow away almost any built-in method in the language
• "0" and "false" are truthy values
• + symbol (unary operator) overloaded for addition and concatenation
• auto semicolon insertion
• new required for object instantiation vs function reference with no error
• new Boolean(false) is true
• global vars infect you everywhere
• oh and don't forget all browsers implement it a little bit differently just like CSS—especially critical features like event handlers, e.g. click