From 193c1ae9cf860dc8db9c1d2c252478d504efa511 Mon Sep 17 00:00:00 2001
From: yangjin <kingyouge@gmail.com>
Date: Thu, 14 Nov 2019 00:17:48 +0800
Subject: [PATCH] =?UTF-8?q?feat:=20=E6=B7=BB=E5=8A=A0=E5=AE=9E=E7=8E=B0=20?=
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diff --git "a/docs/javaScript/\345\256\236\347\216\260instanceof.md" "b/docs/javaScript/\345\256\236\347\216\260instanceof.md"
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--- "a/docs/javaScript/\345\256\236\347\216\260instanceof.md"
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+# 实现 instanceof
+
+`instanceof` 用于判断构造函数的 `prototype` 属性是否出现在一个对象的原型链中。
+
+```js
+function Car(make, model, year) {
+  this.make = make;
+  this.model = model;
+  this.year = year;
+}
+var auto = new Car('Honda', 'Accord', 1998);
+console.log(auto instanceof Car); // true
+console.log(auto instanceof Object); // true
+```
+## instanceof
+
+```js
+/**
+ * instanceof
+ *
+ * @param {Object} obj 需要判断的对象.
+ * @param {Function} ctor 构造函数.
+ * @returns {Boolean} 返回判断结果.
+ */
+function instanceof(obj, ctor) {
+  var proto = obj.__proto__;
+  var prototype = ctor.prototype;
+  while (true) {
+    if (proto == null) return false;
+    if (proto == prototype) return true;
+    proto = proto.__proto__;
+  }
+}
+```
+
+## 参考
+
+- [instanceof](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/instanceof)
+- [instanceof原理](https://juejin.im/post/5b7f64be51882542c83476f0)
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