An alias for @property, except that it has “smarter” default options and a different shorthand parameter. It’s generally recommended over @property for custom component development, but its default behavior may be unexpected for newcomers:

  • The initial value is not undefined but depends on the type (see next section).
  • All values will be automatically converted to the expected type (if possible).
  • The property can not contain a plain object, but a plain object may be set if it can be converted to the type of the property.
  • If set to null or undefined the property is reset to its initial value.
  • If set to a object, any change event fired by that object will cause a change event for this property to be fired as well.
  • If the property contains an array and is set to another array that is shallow-equal (has the same length and entries), the property will keep the current value.
  • If used in a JavaScript file (or if the type can not be inferred at runtime in a TypeScript file), the type of the property must be given via @prop(Class) or @prop({type: Class}), where Class may also be Number, String or Boolean to represent primitives. Without type information a warning will be printed the property and all type-specific features (conversion, initial value, type checks) will be disabled.

For details follow the links in the table below.

@prop (no parameter)

The following table shows how @prop differs in its default configuration from @property:

Option @property @prop
type not set not set
typeGuard not set not set
default not set depends on type*
nullable true depends on type**
equals 'strict' 'auto'
convert 'off' 'auto'
observe false true

*) The default is '' (empty string) for strings, 0 for numbers, false for booleans and null for all other types. *) nullable is false only for primitive types (number, boolean, string and subsets thereof).


A shorthand for @prop({type: type}).


color: ColorValue;

/** @type {string} */
@prop(String) str;


Like @prop, but allows to override the default values just like with @property.