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undefined ↔ Primitive Value to rep Variable "not initialized" or "not existing" (for object property)

Argument​

Value import as Parameter input to function

References​

  1. Primitive Value ↔ undefined, null, number, bigint, boolean, string, symbol

  2. UNNBBSS ↔ undefined, null, number, bigint, boolean, string, symbol

  3. ?? ↔ Nullish Coalescing Operator to assign left calling Operand if !== null/undefined, else assign fallback value (right Operand)

  4. void ↔ JS Operator to evalute Operand as Expression & return undefined

  5. use ": [void](void)" for functions that ↔ should return null/undefined

  6. Optional Chaining ↔ JS Syntax to conditionally call Chain or Dot Notation if function/property exists, else return undefined

  7. "strictNullChecks": true ↔ to throw Exception when access Variable which potentially be null/undefined

  8. Non-Null Assertion Operator ↔ postfix ! Type Assertion to Assert that Variable ≠ undefined || null