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.
If you’ve spent more than 48 hours with JavaScript, you’ve probably uttered the phrase: “Wait… why did it do that?”
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.
const bound = show.bind({hello: "world"}); bound(); // {hello: "world"}
These quirks are frustrating until you understand why they exist. Once you do, you stop fighting the language and start leveraging it.
console.log(typeof NaN); // "number" According to the IEEE 754 floating-point spec (which JS uses), NaN is a numeric data type that represents an invalid number. It’s a number that isn’t a number. The weirdness doesn't stop there:
const obj = { show }; obj.show(); // obj
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.
If you’ve spent more than 48 hours with JavaScript, you’ve probably uttered the phrase: “Wait… why did it do that?”
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.
const bound = show.bind({hello: "world"}); bound(); // {hello: "world"}
These quirks are frustrating until you understand why they exist. Once you do, you stop fighting the language and start leveraging it.
console.log(typeof NaN); // "number" According to the IEEE 754 floating-point spec (which JS uses), NaN is a numeric data type that represents an invalid number. It’s a number that isn’t a number. The weirdness doesn't stop there:
const obj = { show }; obj.show(); // obj
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