Even with strictNullChecks enabled, by default TypeScript assumes array access will never return undefined (unless undefined is part of the array type).

July 17, 2024 - In this example, we use the “===” and “!==” operators to check if the variables x and y are strictly not equal to null and undefined, respectively. If they are not strictly equal, we can safely use the variables without causing a runtime ...

February 27, 2024 - Another way to check for null or undefined is to use the nullish coalescing operator (??), which was introduced in TypeScript 3.7. If the left-hand side of the operation is non-null it returns that, otherwise it returns the right-hand side otherwise.

November 25, 2024 - TypeScript understands a number of these kinds of checks and can use them to narrow the picture of what types can possibly make it through to a specific bit of code. We can use a typeof check against the bar property to see if it is undefined.

July 23, 2025 - We can use typeof or '==' or '===' to check if a variable is null or undefined in typescript.

January 2, 2021 - The correct way to check if something is undefined in JavaScript / TypeScript: Use the typeof operator!

Effectively, null and undefined were valid values of every type and it wasn’t possible to specifically exclude them (and therefore not possible to detect erroneous use of them). strictNullChecks switches to a new strict null checking mode.

January 21, 2025 - javascript // void 0 always returns undefined let myVar; if (myVar === void 0) { console.log('myVar is undefined'); } // Why use void 0? // In old JavaScript, undefined could be reassigned // void 0 is guaranteed to return undefined ... TypeScript, a superset of JavaScript, provides static type checking at compile time, which eliminates many runtime errors and ensures robust code.

March 10, 2024 - The logical AND operator (&&) evaluates to false if the left operand is false or undefined. You can use this in conjunction with a check for another value to ensure both conditions are met.

June 8, 2023 - The easiest way to check if a value is either undefined or null is by using the equality operator (==). The equality operator performs type coercion, which means it converts the operands to the same type before making the comparison.

TypeScript flags “possibly ... safely handled. The solution is to either explicitly check for the value before usage or pass the value as a required argument to functions, ensuring type safety and preventing runtime ...

January 10, 2026 - The global scope is bound to the global object, so checking the existence of a variable in the global context can be done by checking the existence of a property on the global object, such as by using the in operator: ... However, none of the techniques above work if the variable is declared with let, const, or other lexical declarations. Using typeof before the line of declaration still produces a ReferenceError, due to the temporal dead zone (TDZ). ... if (typeof z === "undefined") { // Uncaught ReferenceError: Cannot access 'z' before initialization } let z = 1;

March 28, 2023 - Another way to check for null or undefined is to use the nullish coalescing operator (??), which was introduced in TypeScript 3.7.

February 28, 2024 - This design choice is inherited from JavaScript, providing flexibility in indicating the absence of a value (null) versus an uninitialized variable (undefined). ... Zipy offers proactive error monitoring and session replay capabilities, allowing developers to see exactly what led to an error, including the user's actions and the application state at the time of the error. Understand TypeScript's Type System: Leveraging TypeScript's strict typing can prevent many Null or Undefined Value Errors.

July 21, 2018 - I have a function that required a non-undefined argument. I do the required field check in a separate function and if the required variable is undefined or null, it should throw an error and the variable is not really used.

February 18, 2025 - In JavaScript, undefined is the default value for variables that have been declared but not initialized. On the other hand, null is an intentional assignment that explicitly indicates the absence of a value. ... This article covers different ways to check if a variable is undefined, helping you write code that handles these situations smoothly.

March 15, 2023 - The value null indicates that you know that the field does not have a value. It is an intentional absence of value. Whenever we declare a variable without initializing it with a value, TypeScript initializes it as undefined.