Override the behavior of instanceof
Written byPhuoc Nguyen
Created
23 Feb, 2021
Category
Trick
Tags
JavaScript
`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:js
class PrimitiveNumber {
static [Symbol.hasInstance](value) {
return typeof value === 'number';
}
}
12345 instanceof PrimitiveNumber; // true
'helloworld' instanceof PrimitiveNumber; // false
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Phước Nguyễn