Quartz sync: May 6, 2024, 10:40 PM

content/20201113094246-javascript_instanceof_operator.md

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+---
+id: 54c58f54-526f-4838-92c5-1a70d6b17a3c
+title: JavaScript Instanceof Operator
+---
+
+# Description
+
+Sometimes you want to know whether an [object](20200826201605-objects)
+was derived from a specific [class](20201008090316-class_notation). To
+do this one can use the `instanceof`
+[operator](20200613170705-operators_in_javascript).
+
+# Syntax
+
+``` javascript
+class Parent {
+  constructor(name, parentChild = "Parent") {
+    this.parentChild = parentChild;
+    this.name = name;
+  }
+
+  speak(line) {
+    console.log(`${this.parentChild} ${this.name} says '${line}'`);
+  }
+}
+
+class Child extends Parent {
+  constructor(name) {
+    super(name, "Child");
+  }
+}
+
+let parent = new Parent("Father");
+let child = new Child("Gregory");
+
+console.log(parent instanceof Parent); // true
+console.log(parent instanceof Child); // false
+console.log(child instanceof Parent); // true
+console.log(child instanceof Child); // true
+```