# 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|String|Number|Boolean` | No | Child [vnodes](vnodes.md). Can be written as [splat arguments](signatures.md#splats) **returns** | `Vnode` | | A [vnode](vnodes.md) 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` 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` indicates that the argument must be an object, whose keys are strings and values are [components](components.md) 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](vnodes.md) 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`](hyperscript.md) if given, defaults to `"a"`. `attributes.options` | `Object` | No | This sets the options passed to [`m.route.set`](#mrouteset). `attributes` | `Object` | No | Other attributes to apply to the returned vnode may be passed. `children` | `Array|String|Number|Boolean` | No | Child [vnodes](vnodes.md) for this link. **returns** | `Vnode` | | A [vnode](vnodes.md). Children here, if specified, are assumed to be able to be written as [splat arguments](#splats), 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](vnodes.md)