How to read signatures

Signature sections typically look like this:

vnode = m(selector, attributes, children)

Argument	Type	Required	Description
selector	String|Object	Yes	A CSS selector or a component
attributes	Object	No	HTML attributes or element properties
children	Array<Vnode>|String|Number|Boolean	No	Child vnodes. Can be written as splat arguments
returns	Vnode		A vnode

The signature line above the table indicates the general syntax of the method, showing the name of the method, the order of its arguments and a suggested variable name for its return value.

The Argument column in the table indicates which part of the signature is explained by the respective table row. The returns row displays information about the return value of the method.

The Type column indicates the expected type for the argument.

A pipe (|) indicates that an argument is valid if it has any of the listed types. For example, String|Object indicates that selector can be a string OR an object.

Angled brackets (< >) after an Array indicate the expected type for array items. For exampe, Array<String> indicates that the argument must be an array and that all items in that array must be strings. Angled brackets after an Object indicate a map. For example, Object<String,Component> indicates that the argument must be an object, whose keys are strings and values are components

Sometimes non-native types may appear to indicate that a specific object signature is required. For example, Vnode is an object that has a virtual DOM node structure.

The Required column indicates whether an argument is required or optional. If an argument is optional, you may set it to null or undefined, or omit it altogether, such that the next argument appears in its place.

Optional arguments

Function arguments surrounded by square brackets [ ] are optional. In the example below, url is an optional argument:

m.request([url,] options)

Splats

A splat argument means that if the argument is an array, you can omit the square brackets and have a variable number of arguments in the method instead.

In the example at the top, this means that m("div", {id: "foo"}, ["a", "b", "c"]) can also be written as m("div", {id: "foo"}, "a", "b", "c").

Splats are useful in some compile-to-JS languages such as CoffeeScript, and also allow helpful shorthands for some common use cases.

Function signatures

Functions are denoted with an arrow (->). The left side of the arrow indicates the types of the input arguments and the right side indicates the type for the return value.

For example, parseFloat has the signature String -> Number, i.e. it takes a string as input and returns a number as output.

Functions with multiple arguments are denoted with parenthesis: (String, Array) -> Number

Component signatures

Components are denoted via calls to m, but with the initial selector argument set to a constant named in the relevant prose:

vnode = m(m.route.Link, attributes, children)

Argument	Type	Required	Description
attributes.href	Object	Yes	The target route to navigate to.
attributes.selector	String|Object|Function	No	This sets the tag name to use. Must be a valid selector for m if given, defaults to "a".
attributes.options	Object	No	This sets the options passed to m.route.set.
attributes	Object	No	Other attributes to apply to the returned vnode may be passed.
children	Array<Vnode>|String|Number|Boolean	No	Child vnodes for this link.
returns	Vnode		A vnode.

Children here, if specified, are assumed to be able to be written as splat arguments, unless otherwise specified in prose.

An element with no sensible children and/or attributes may choose to elide the relevant parameter entirely:

vnode = m(Component, attributes)

Argument	Type	Required	Description
attributes.href	Object	Yes	The
attributes	Object	No	Other attributes to apply to the returned vnode
returns	Vnode		A vnode