Javascript Weird Parts May 2026

function show() { console.log(this); } show(); // window (or global in Node) new show(); // {} (the new instance)

Arrow functions don't have their own this —they inherit from the parent scope. That’s often a lifesaver, but it’s another thing to memorize. Every value in JS is inherently truthy or falsy. There are exactly 8 falsy values :

const bound = show.bind({hello: "world"}); bound(); // {hello: "world"} javascript weird parts

Use a small epsilon or multiply by powers of 10 for money calculations (or use BigInt for integers). 5. Automatic Semicolon Insertion (ASI) JavaScript tries to be helpful. Sometimes too helpful.

console.log(1 + "2"); // "12" (string) console.log(1 + 2 + "3"); // "33" (evaluates left to right: 3 + "3") console.log([] + []); // "" (empty string) console.log([] + {}); // "[object Object]" console.log({} + []); // 0 (Wait, run this in a console... yes, 0) The last one is a parsing edge case where {} is interpreted as an empty code block, not an object. This one angers accountants and mathematicians equally. function show() { console

function getObject() { return { value: 42 } } console.log(getObject()); // undefined

false , 0 , -0 , 0n (BigInt zero), "" , null , undefined , NaN . There are exactly 8 falsy values : const bound = show

console.log(0.1 + 0.2); // 0.30000000000000004 console.log(0.1 + 0.2 === 0.3); // false Floating-point math. JavaScript uses binary floating point; 0.1 in binary is a repeating fraction (like 1/3 in decimal). It can't be represented exactly.