!== null vs !== undefined in Typescript or Javascript, how to check for both at once?

The choice between !== undefined and !== null depends on the context and what you’re trying to check.

Key Differences:

1. undefined:
   • A variable or property that has been declared but not assigned a value.
   • A function parameter that was not provided when the function was called.
   • A property that doesn’t exist in an object.
2. null:
   • An explicit value that represents “no value” or “empty.”
   • Often used to intentionally signify the absence of a value.

When to Use:

1. Use !== undefined when:
   • You’re dealing with cases where a variable might be uninitialized or omitted.
   • Checking whether a parameter was passed to a function.

   if (value !== undefined) {
     // Do something
   }
   

2. Use !== null when:
   • You explicitly assign null to indicate “no value.”
   • Checking against a value explicitly set as null.

   if (value !== null) {
     // Do something
   }
   

3. Use both (value != null) when:
   • You want to check for both null and undefined together, since null and undefined are considered equal in loose equality (==).
   • Commonly used when you don’t care about the specific type of “empty.”

   if (value != null) {
     // Do something if value is not null or undefined
   }
   

Best Practice:

• Prefer strict equality checks (!== or ===) for better type safety and clarity.
• Use != null only when you explicitly want to check for both null and undefined.

For your example:

• offerPrice !== undefined is correct if you’re checking whether the parameter was passed.
• If offerPrice might explicitly be null, you should use offerPrice != null to handle both cases.