fragment(attrs, children)

• Core
  • m
  • m.render
  • m.mount
  • m.route
  • m.request
  • m.jsonp
  • m.parseQueryString
  • m.buildQueryString
  • m.withAttr
  • m.trust
  • m.fragment
    • Description
    • Signature
    • How it works
  • m.redraw
  • m.version
  • Promise
• Optional
  • Stream
• Tooling
  • Ospec

Description

Allows attaching lifecycle methods to a fragment vnode

var groupVisible = true
var log = function() {
    console.log("group is now visible")
}

m("ul", [
    m("li", "child 1"),
    m("li", "child 2"),
    groupVisible ? m.fragment({oninit: log}, [
        // a fragment containing two elements
        m("li", "child 3"),
        m("li", "child 4"),
    ]) : null
])

Signature

Generates a fragment vnode

vnode = m.fragment(attrs, children)

How to read signatures

How it works

m.fragment() creates a fragment vnode with attributes. It is meant for advanced use cases involving keys or lifecyle methods.

A fragment vnode represents a list of DOM elements. If you want a regular element vnode that represents only one DOM element, you should use m() instead.

Normally you can use simple arrays instead to denote a list of nodes:

var groupVisible = true

m("ul", [
    m("li", "child 1"),
    m("li", "child 2"),
    groupVisible ? [
        // a fragment containing two elements
        m("li", "child 3"),
        m("li", "child 4"),
    ] : null
])

However, Javascript arrays cannot be keyed or hold lifecycle methods. One option would be to create a wrapper element to host the key or lifecycle method, but sometimes it is not desirable to have an extra element (for example in complex table structures). In those cases, a fragment vnode can be used instead.

There are a few benefits that come from using m.fragment instead of handwriting a vnode object structure: m.fragment creates monomorphic objects, which have better performance characteristics than creating objects dynamically. In addition, using m.fragment makes your intentions clear to other developers, and it makes it less likely that you'll mistakenly set attributes on the vnode object itself rather than on its attrs map.