TypeError: Cannot set properties of undefined/null

Causes de cette erreur

You tried to assign a property to a value that is null or undefined. This happens when the parent object was never initialized, a function returned null instead of an object, or a variable was not properly assigned before use.

Comment la corriger

Initialize the object before setting properties on it. Check that functions return valid objects rather than null/undefined. Add defensive checks: if (obj) { obj.prop = value; }. Use default values during initialization.

let obj = null; obj.key = 'value'; // TypeError