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Override the behavior of instanceof

Written byPhuoc Nguyen
23 Feb, 2021
`instanceof` doesn't work for primitive types.
If you want to use `instanceof` all the time, then you can override the behavior of `instanceof` by implementing a static method with the key of `Symbol.hasInstance`. In the following code, we create a class called `PrimitiveNumber` that checks if a value is a number:
class PrimitiveNumber {
static [Symbol.hasInstance](value) {
return typeof value === 'number';

12345 instanceof PrimitiveNumber; // true
'helloworld' instanceof PrimitiveNumber; // false

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