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56 lines
3.1 KiB
Markdown
56 lines
3.1 KiB
Markdown
# How to read signatures
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Signature sections typically look like this:
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`vnode = m(selector, attributes, children)`
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Argument | Type | Required | Description
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------------ | ------------------------------------ | -------- | ---
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`selector` | `String|Object` | Yes | A CSS selector or a component
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`attributes` | `Object` | No | HTML attributes or element properties
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`children` | `Array<Vnode>|String|Number|Boolean` | No | Child [vnodes](vnodes.md). Can be written as [splat arguments](signatures.md#splats)
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**returns** | `Vnode` | | A [vnode](vnodes.md)
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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.
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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.
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The **Type** column indicates the expected type for the argument.
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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.
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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](components.md)
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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.
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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.
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---
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### Optional arguments
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Function arguments surrounded by square brackets `[ ]` are optional. In the example below, `url` is an optional argument:
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`m.request([url,] options)`
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---
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### Splats
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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.
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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")`.
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Splats are useful in some compile-to-js languages such as Coffeescript, and also allow helpful shorthands for some common use cases.
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---
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### Function signatures
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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.
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For example, `parseFloat` has the signature `String -> Number`, i.e. it takes a string as input and returns a number as output.
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Functions with multiple arguments are denoted with parenthesis: `(String, Array) -> Number`
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