console.log([] + []); // "" console.log([] + {}); // "[object Object]" console.log({} + []); // 0 (in Chrome console) The circulating in forums and tweets is often phrased as: "Angela Yu once broke JavaScript by making it think 'Angela' minus 'Yu' equals 'Not a Number' – and then laughed while students questioned their life choices." So if someone says "Angela Yu JavaScript story" , they likely mean the type coercion horror story from her bootcamp that haunts beginners (and amuses veterans).

This is a reference to a famous and rather terrifying (but educational) JavaScript story involving and her "JS is a weird language" lesson.

// But then she shows the weird part: let weird = "Angela" - "Yu"; // NaN (Not a Number) let weird2 = "Angela" * 1; // NaN let weird3 = [] + []; // "" (empty string) let weird4 = [] + {}; // "[object Object]" let weird5 = {} + []; // 0 (in some consoles, due to {} being interpreted as a block)

Angela Yu is the lead instructor for the popular on Udemy. In one of her most memorable sections, she demonstrates JavaScript's type coercion and quirks to shock students into paying attention.

The actual she tells isn't about a narrative plot, but a teaching moment : She asks students to predict the output of:

The specific story/code snippet often shared by her students goes like this:

// The "Angela Yu" classic example: let result = "Angela" + " " + "Yu"; // "Angela Yu" - normal