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Expand README for plugin-transform-instanceof [skip ci] (#7827)

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Michael Mantel 2018-04-27 13:21:09 -07:00 committed by Brian Ng
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packages/babel-plugin-transform-instanceof/README.md
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@ -1,5 +1,29 @@
# @babel/plugin-transform-instanceof
> Wraps `instanceof` expressions to allow constructors to customize the logic with a `Symbol.hasInstance` method
## Example
**In**
```javascript
foo instanceof Bar;
```
**Out**
```javascript
function _instanceof(left, right) {
if (right != null && typeof Symbol !== "undefined" && right[Symbol.hasInstance]) {
return right[Symbol.hasInstance](left);
} else {
return left instanceof right;
}
}
_instanceof(foo, Bar);
```
## Installation
```sh
@ -31,3 +55,8 @@ require("@babel/core").transform("code", {
plugins: ["@babel/plugin-transform-instanceof"]
});
```
## References
* [ES6 Spec: InstanceOf Operator Semantics](https://www.ecma-international.org/ecma-262/6.0/#sec-instanceofoperator)
* [MDN: Symbol.hasInstance](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/hasInstance)