JavaScript and QML Checks

To run static checks, go to Tools > QML/JS > Run Checks or press Ctrl+Shift+C.

View the results in the QML and QML Analysis filters in Issues.

Enabling and Disabling Messages

To enable and disable QML and JavaScript messages:

Go to Preferences > Qt Quick > QML/JS Editing.
Select Use customized static analyzer.
In Enabled, select the messages that you want to see.
To disable messages for non-Qt Quick UI files, select them in Disable messages for non Qt Quick UI. You cannot enable messages just for non-Qt Quick UI files.

JavaScript and QML Error Codes

Many of the error messages are similar to the ones in Douglas Crockford's JSLint tool. For more information about JSLint errors, see JSLint Error Explanations.

Id	Severity	Message	Description
M1	Error	Invalid value for enum
M2	Error	Enum value must be a string or a number
M3	Error	Number value expected
M4	Error	Boolean value expected
M5	Error	String value expected
M6	Error	Invalid URL
M7	Warning	File or directory does not exist
M8	Error	Invalid color
M9	Error	Anchor line expected
M10	Error	Duplicate property binding	See also: Duplicate key '{a}'.
M11	Error	Id expected	See also: Expected an identifier and instead saw '{a}' (a reserved word).
M14	Error	Invalid id	See also: Expected an identifier and instead saw '{a}' (a reserved word).
M15	Error	Duplicate id	Ids in a file must be unique. See also: Duplicate key '{a}'.
M16	Error	Invalid property name `name`
M17	Error	`Name` does not have members
M18	Error	`Field` is not a member of `object`
M19	Warning	Assignment in condition	It could be a typing error. If it is intentional, wrap the assignment in parentheses.
M20	Warning	Unterminated non-empty case block	Case blocks should either be empty or end in a flow control statement such as `break`, `return` or `continue`. Alternatively you can indicate intentional fall through by ending with a `// fall through` comment.
M23	Warning	Do not use `eval`	See also: eval is evil.
M28	Warning	Unreachable	Indicates that the underlined statement will never be executed.
M29	Warning	Do not use `with`	See also: Unexpected 'with'.
M30	Warning	Do not use comma expressions
M31	Warning	Unnecessary message suppression
M103	Warning	`Name` is already a formal parameter
M104	Warning	`Name` is already a function
M105	Warning	Var `name` is used before its declaration
M106	Warning	`Name` already is a var
M107	Warning	`Name` is declared more than once	Variables declared in a function are always visible everywhere in the function, even when declared in nested blocks or `for` statement conditions. Redeclaring a variable has no effect.
M108	Warning	Function `name` is used before its declaration	See also: {a} was used before it was defined.
M109	Warning	Do not use `Boolean` as a constructor	See also: Do not use {a} as a constructor.
M110	Warning	Do not use `String` as a constructor	See also: Do not use {a} as a constructor.
M111	Warning	Do not use `Object` as a constructor	See also: Do not use {a} as a constructor.
M112	Warning	Do not use `Array` as a constructor	See also: Do not use {a} as a constructor.
M113	Warning	Do not use `Function` as a constructor	See also: Do not use {a} as a constructor.
M114	Hint	The `function` keyword and the opening parenthesis should be separated by a single space	See also: Expected exactly one space between {a} and {b}.
M115	Warning	Do not use stand-alone blocks	Blocks do not affect variable scoping. Thus blocks that are not associated to `if`, `while`, etc. have no effect and should be avoided.
M116	Warning	Do not use void expressions
M117	Warning	Confusing pluses	See also: Confusing pluses.
M119	Warning	Confusing minuses	See also: Confusing minuses.
M121	Hint	Declare all function vars on a single line
M123	Hint	Unnecessary parentheses
M126	Warning	`==` and `!=` may perform type coercion, use `===` or `!==` to avoid it	The non-strict equality comparison is allowed to convert its arguments to a common type. That can lead to unexpected results such as `' \t\r\n' == 0` being true. Use the strict equality operators `===` and `!==` and be explicit about conversions you require.
M127	Warning	Expression statements should be assignments, calls or delete expressions only
M128	Error	A state cannot have the specified child item
M129	Error	Type cannot be instantiated recursively
M201	Hint	Place var declarations at the start of a function	See also: Move 'var' declarations to the top of the function.
M202	Hint	Use only one statement per line
M220	Error	This type (type name) is not supported as a root element of a UI file (.ui.qml)	For more information about supported QML types, see UI Files.
M221	Error	This type (type name) is not supported in a UI file (.ui.qml)	For more information about supported QML types, see UI Files.
M222	Error	Functions are not supported in a UI file (.ui.qml)	For a list of supported JavaScript functions, see Supported Methods.
M223	Error	JavaScript blocks are not supported in a UI file (.ui.qml)	For more information about supported features, see UI Files.
M224	Error	Behavior type is not supported in a UI file (.ui.qml)	For more information about supported QML types, see UI Files.
M225	Error	States are only supported in the root item in a UI file (.ui.qml)	For more information about supported features, see UI Files.
M226	Error	Referencing the parent of the root item is not supported in a UI file (.ui.qml)	For more information about supported features, see UI Files.
M227	Error	Do not mix translation functions in a UI file (.ui.qml)	Even though several different translation functions, such as `qsTr` and `qsTrId` are supported, you should pick one and use it consistently within a UI file. For more information, see Qt QML Methods.
M300	Error	Unknown component
M301	Error	Could not resolve the prototype `name` of `object`
M302	Error	Could not resolve the prototype `name`
M303	Error	Prototype cycle, the last non-repeated component is `name`
M304	Error	Invalid property type `name`
M305	Warning	`==` and `!=` perform type coercion, use `===` or `!==` to avoid it	See M126.
M306	Warning	Calls of functions that start with an uppercase letter should use `new`	By convention, functions that start with an uppercase letter are constructor functions that should only be used with `new`.
M307	Warning	Use `new` only with functions that start with an uppercase letter	See also: Do not use {a} as a constructor.
M308	Warning	Do not use `Number` as a constructor	See also: Do not use {a} as a constructor.
M309	Hint	Use spaces around binary operators
M310	Warning	Unintentional empty block, use ({}) for empty object literal
M311	Hint	Use `type` instead of `var` or `variant` to improve performance
M312	Error	Missing property `number`
M313	Error	Object value expected
M314	Error	Array value expected
M315	Error	`Value` value expected
M316	Error	Maximum number value is `number`
M317	Error	Minimum number value is `number`
M318	Error	Maximum number value is exclusive
M319	Error	Minimum number value is exclusive
M320	Error	String value does not match required pattern
M321	Error	Minimum string value length is `number`
M322	Error	Maximum string value length is `number`
M323	Error	`Number` elements expected in array value	See also: The array literal notation [] is preferable.
M324	Error	Hit maximum recursion limit visiting AST, the code model will be unreliable and most likely invalid
M326	Error	Components are only allowed to have a single child element	For more information, see Component.
M327	Warning	Components require a child element	For more information, see Component.
M400	Warning	Duplicate import	An import statement has been added twice. For more information, see Import Statements.
M401	Error	Do not reference the root item as alias	The alias property cannot reference the root component directly. Create an instance of the component instead.
M402	Warning	Avoid referencing the root item in a hierarchy	The alias property cannot reference the root component in a hierarchy. Create an instance of the component instead.
M403	Error	A when condition cannot contain an object	Set the `when` condition to an expression that evaluates to `true` when the condition is met.

Resetting the Code Model

If you see the following error messages after you add a new QML module, try building the project and then resetting the code model:

QML module not found.
Unknown Component (M300).

To see an error message, move the mouse pointer over code that Qt Creator underlines in the code editor or when you open a QML file in Qt Design Studio.

To reset the code model, select Tools > QML/JS > Reset Code Model.

Reference

Copyright © The Qt Company Ltd. and other contributors. Documentation contributions included herein are the copyrights of their respective owners. The documentation provided herein is licensed under the terms of the GNU Free Documentation License version 1.3 as published by the Free Software Foundation. Qt and respective logos are trademarks of The Qt Company Ltd in Finland and/or other countries worldwide. All other trademarks are property of their respective owners.