Completed Concept Entry for Javascript: Optional Chaining #5805 (#5826)

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Author: nbarnhouse

content/javascript/concepts/optional-chaining/optional-chaining.md

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+---
+Title: 'Optional Chaining'
+Description: 'The optional chaining operator allows safe access to nested object properties or methods without having to explicitly check if intermediate properties exist.'
+Subjects:
+  - 'Web Development'
+  - 'Computer Science'
+Tags:
+  - 'Data'
+  - 'Operators'
+CatalogContent:
+  - 'introduction-to-javascript'
+  - 'paths/front-end-engineer-career-path'
+---
+
+The **optional chaining** (**`?.`**) operator simplifies comparing multiple data properties in a chain of connected objects. This is especially valuable if any of the properties are `null`, as the operator will return `undefined` instead of throwing an error.
+
+Optional chaning can be used to validate nested object properties, call optional functions or methods on optional objects, accessing array elements, and more.
+
+The primary benefits of using optional chaining instead of regular syntax include simplifying the code to achieve the same result, making it easier to read, protecting against runtime errors, and enhancing maintainability.
+
+## Syntax
+
+The basic syntax for using optional chaining is as follows:
+
+```pseudo
+// To access an object property
+object?.property;
+
+//To access an element in an array
+array?.[index];
+
+//To invoke a function (if it exists)
+object?.method?.();
+```
+
+## Examples
+
+### Accessing Object Properties
+
+To search for the `state` object of `person`:
+
+```js
+const person = {
+  name: 'Alice',
+  gender: 'Female',
+  age: 12,
+  address: {
+    street: '1111 Palm Ave',
+    city: 'Broken Arrow',
+    state1: 'Oklahoma',
+  },
+  favoriteFoods: ['pizza', 'ice cream', 'cake'],
+  commonPhrase: function () {
+    return `${this.name} always says "I love ${this.address.state1}."`;
+  },
+};
+
+// Regular syntax for checking if the state1 property exists
+const state1Regular = person && person.address && person.address.state1;
+console.log(`State (regular syntax) is: ${state1Regular}`);
+
+// This can be rewritten as:
+const state1Chaining = person?.address?.state1;
+console.log(`State (optional chaining) is: ${state1Chaining}`);
+```
+
+The output of the above code will be as follows:
+
+```shell
+State (regular syntax) is: Oklahoma
+State (optional chaining) is: Oklahoma
+```
+
+### Accessing Array Elements
+
+To search for the `cake` in the `favoriteFoods` array of `person`:
+
+```js
+const person = {
+  name: 'Alice',
+  gender: 'Female',
+  age: 12,
+  address: {
+    street: '1111 Palm Ave',
+    city: 'Broken Arrow',
+    state1: 'Oklahoma',
+  },
+  favoriteFoods: ['pizza', 'ice cream', 'cake'],
+  commonPhrase: function () {
+    return `${this.name} always says "I love ${this.address.state1}."`;
+  },
+};
+
+// Regular Syntax for searching favorite food
+const foodRegular =
+  person &&
+  person.favoriteFoods &&
+  person.favoriteFoods.find((item) => item === 'cake');
+console.log(`Favorite Food (regular syntax) is: ${foodRegular}`);
+
+// This can be rewritten as:
+const foodChaining = person?.favoriteFoods.find((item) => item === 'cake');
+console.log(`Favorite Food (optional chaining) is: ${foodChaining}`);
+```
+
+The output of the above code will be as follows:
+
+```shell
+Favorite Food (regular syntax) is: cake
+Favorite Food (optional chaining) is: cake
+```
+
+### Accessing Object Functions
+
+To determine if the `commonPhrase` function exists in `person` before invoking it:
+
+```js
+//Regular Syntax
+if (person && typeof person.commonPhrase === 'function') {
+  const phrase = person.commonPhrase();
+  console.log(`${phrase}`);
+}
+
+//This can be rewritten as:
+const phrase = person?.commonPhrase?.();
+console.log(`${phrase}`);
+```
+
+The output of the above code will be as follows:
+
+```shell
+Alice always says "I love Oklahoma."
+Alice always says "I love Oklahoma."
+```
+
+## Codebyte Example
+
+Run the following example and compare the regular syntax of conditional statements and optional chaining on a more complex data set:
+
+```codebyte/javascript
+const people = [
+  {
+    name: "Blake",
+    gender: "Male",
+    age: null,
+    address: {
+      street: "456 Maple Dr",
+      city: "Austin",
+      state: "Texas"
+    }
+  },
+  {
+    name: "Eve",
+    gender: "Female",
+    age: 15,
+    address: {
+      street: "789 Birch Ln",
+      city: "",
+      state: "Colorado"
+    }
+  },
+  null,
+  {
+    name: "David",
+    gender: "Male",
+    age: 72,
+    address: {
+      street: "123 Acorn St",
+      city: "Tampa",
+      state: "Florida"
+    }
+  },
+  {
+    name: "Jospeh",
+    gender: "Male",
+    age: 9,
+    address: {
+      street: "987 Pine Ave",
+      city: "Taos",
+      state: "New Mexico"
+    }
+  }
+];
+
+console.log("Using Regular Syntax for City:");
+people.forEach((person, index) => {
+  const city = person && person.address && person.address.city;
+  console.log(`Person ${index + 1}: City: ${city ?? "Not Available"}`);
+});
+
+console.log("\nUsing Optional Chaining for Age:");
+people.forEach((person, index) => {
+  const age = person?.age;
+  console.log(`Person ${index + 1}: Age: ${age ?? "Not Available"}`);
+});
+```