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

content/20201113090337-javascript_in_operator.md

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+---
+id: 4cd0d42b-3414-4402-95f1-7498fbc52c20
+title: JavaScript In Operator
+---
+
+# Description
+
+`in`[^1] tells us if indices inside an [array](20200826201029-arrays) or
+[object](20200826201605-objects) have no associated element.
+
+# Syntax
+
+``` javascript
+const arr = ['a',,'b']
+console.log(0 in arr) // true
+console.log(1 in arr) // false
+console.log(2 in arr) // true
+console.log(arr[1]) // undefined
+```
+
+``` javascript
+const car = { make: "Honda", model: "Accord", year: 1998 };
+
+console.log("make" in car); // true
+
+delete car.make;
+if ("make" in car === false) {
+  car.make = "Suzuki";
+}
+
+console.log(car.make); //Suzuki
+```
+
+# Footnotes
+
+[^1]: <https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/in>