Summary  
This chapter discusses safe handling of potentially null DOM elements in TypeScript by using optional chaining and non-null assertion operators to prevent runtime errors when querying the DOM.

General domain of usage  
Client-side web applications

Y29uc3QgaW5wdXQgPSBkb2N1bWVudC5xdWVyeVNlbGVjdG9yKCdpbnB1dCN1c2VybmFtZScpOwoKaWYgKGlucHV0ICE9PSBudWxsKSB7CiAgLy8gU2FmZSB0byBhY2Nlc3MgcHJvcGVydGllcyBiZWNhdXNlIGlucHV0IGlzIG5vdCBudWxsCiAgaW5wdXQudmFsdWUgPSAnVHlwZVNjcmlwdFVzZXInOwp9IGVsc2UgewogIC8vIEhhbmRsZSB0aGUgY2FzZSB3aGVuIHRoZSBlbGVtZW50IGlzIG5vdCBmb3VuZAogIGNvbnNvbGUubG9nKCdJbnB1dCBlbGVtZW50IG5vdCBmb3VuZC4nKTsKfQ==

When you use `querySelector` or similar DOM methods in TypeScript, the result can be `null` if no element matches the selector. This means you must handle the possibility that the returned node does not exist before accessing its properties. Failing to check for `null` can lead to runtime errors if you try to use a property or method on an object that does not exist.

TypeScript offers features to help you safely work with potentially `null` DOM nodes. **Optional chaining** (`?.`) allows you to access properties or call methods only if the object is not `null` or `undefined`. For example, `input?.value = "TypeScriptUser";` will only set the value if `input` exists. **Non-null assertions** (`!`) tell TypeScript that you are sure the object is not `null` by writing `input!.value = "TypeScriptUser";`. However, using the non-null assertion operator is risky unless you are certain the element exists, because it bypasses TypeScript's safety checks.

Whenever you query the DOM, always consider whether the element might not be present and use these features appropriately to avoid errors and ensure your code remains robust.

Why is it important to check for `null` after querying a DOM node in TypeScript?

Work with the DOM using TypeScript to write safer, clearer, and more predictable front-end code. Apply precise types to elements, events, and form inputs to avoid runtime errors and improve interactivity. Use type-driven patterns to select, update, create, and remove DOM elements with confidence.

Understand how TypeScript interprets DOM elements and why precise typing matters for interactive applications. Learn essential techniques such as type assertions, type guards, and null safety to prevent common DOM-related errors.

Use TypeScript to write safer event-driven code by typing events, handlers, and event targets correctly. Extend these skills to create reliable form validation logic with strongly typed inputs and predictable data handling.

Work with advanced DOM APIs through a type-safe lens. Use generic selectors, update element properties safely, and create or remove DOM nodes with consistent TypeScript patterns that reduce bugs and improve maintainability.

Handling Null DOM Nodes