Error map
Undefined property Warning: Undefined property: Class::$prop
PHP · layer 4, Application & API
Centre: this error. First ring: errors it is linked with (7). Outer ring: what those are linked with. Colours show the layer of a request each error belongs to. Click any dot to re-centre the map on it; hover to follow its connections. The centre dot opens the error page.
Directly related (7)
TypeError: Cannot read properties of undefined (reading 'x')
You tried to access a property on a value that is `undefined` (or `null`) — usually data that hasn’t loaded yet or a wrong proper…
TypeError: Cannot read properties of undefined (reading 'length')
Code checked .length on something that is undefined — typically an array or string that hasn’t loaded.
Warning: Trying to access array offset on value of type null
Code used `$x['key']` where `$x` is null — usually a lookup or function that returned nothing.
TypeError: Cannot convert undefined or null to object
Object.keys/entries/assign was called with undefined or null.
Warning: Undefined variable $x
PHP read a variable that was never assigned in the current scope.
TypeError: Cannot assign to read only property 'x' of object
Code tried to modify a frozen object, a getter-only property, or immutable state.
TypeError: Cannot set properties of undefined (setting 'x')
Code assigned a property on a value that is undefined (or null).
Two steps away (17)
System.NullReferenceException: Object reference not set to an instance of an object
Code dereferenced a variable that is `null` — the .NET equivalent of Java’s NullPointerException.
TypeError: x is not a function
You called something as a function, but its value is not a function (it’s undefined, a string, an object…).
ReferenceError: x is not defined
Code refers to a variable or function name that doesn’t exist in the current scope.
java.lang.ArrayIndexOutOfBoundsException: Index 5 out of bounds for length 5
Code accessed an array index outside 0 … length-1.
TypeError: Cannot read properties of null (reading 'addEventListener')
document.querySelector/getElementById returned null, so the element doesn’t exist when the script runs.
TypeError: x is not iterable
for…of, spread or destructuring was used on something that isn’t an array/iterable.
Warning: Undefined array key / Undefined index
Your code reads an array key that doesn’t exist — common with `$_GET`, `$_POST` and decoded JSON.
TypeError: Reduce of empty array with no initial value
Array.reduce() ran on an empty array without an initial value.
RangeError: Invalid array length
An array was created or resized with a negative, fractional or enormous length.
TypeError: Cannot destructure property 'user' of 'useContext(...)' as it is undefined.
A component read a context with no matching Provider above it.
Warning: Array to string conversion
An array was used where a string is expected — echoing it, concatenating it, or passing it to a string function.
HTTP 409 Conflict
The request conflicts with the current state of the resource — e.g. a duplicate or an edit based on an outdated version.
Warning: A component is changing an uncontrolled input to be controlled
An input’s `value` started as `undefined` (uncontrolled) and later became a defined value (controlled), or vice versa.
java.lang.IllegalStateException
A method was called when the object wasn’t in the right state for it.
RangeError: Maximum call stack size exceeded
A function called itself (directly or indirectly) too many times — usually infinite recursion.
KeyError: 'x'
You accessed a dictionary key that doesn’t exist.
TypeError: 'NoneType' object is not subscriptable
You used `[ ]` on a value that is `None` — typically a function that returned nothing.
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