@gcj-component/vue-virtual-scroll

Table of contents

• Advantages
• Live demos
• How it works
• Simple usage
  • vfor-mode
  • item-mode
  • variable height
• Performance comparison
  • Build time wasted
  • Total memory used
• Attentions
• Props type
• Public methods
• Contributions
• Changelogs

Advantages

• Items are independent.

• Tiny and very easy to use.

• Big data list with high performance.

Live demos

• Build 100,000 items with vfor-mode.

• Build 100,000 items with item-mode.

• Build 100,000 items with variable height.

The main difference between item-mode and vfor-mode is that: item-mode make a higher performance but not very convenient to handle changing data frequently; however, vfor-mode is just the opposite.

Besides, you can also compare the experience which without using virtual-list here: without-virtual-list.

How it works

Simple usage

npm install vue-virtual-scroll-list --save

vfor-mode

All you need to care about is only data!

<template>
  <div>
    <virtual-list :size="40" :remain="8">
      <item v-for="item of items" :key="item.id" />
    </virtual-list>
  </div>
</template>
<script>
  import item from '../item.vue'
  import virtualList from 'vue-virtual-scroll-list'
  export default {
    data () {
      return {
        items: [ {id: 1}, {id: 2}, {id: 3}, ... ]
      }
    },
    components: { item, 'virtual-list': virtualList }
  }
</script>

item-mode

This mode can save a considerable amount of memory and performance. Props item, itemcount and itemprops are both required, you don't need put <item/> with a v-for directive inside virtual-list, just assign it as prop item:

<template>
  <div>
    <virtual-list :size="40" :remain="8"
      :item="item"
      :itemcount="100000"
      :itemprops="getItemprops"
    />
  </div>
</template>
<script>
  import itemComponent from '../item.vue'
  import virtualList from 'vue-virtual-scroll-list'
  export default {
    data () {
      return {
        item: itemComponent,
      }
    },
    methods: {
      getItemprops (itemIndex) {
        // <item/> will render with following data object:
        // https://vuejs.org/v2/guide/render-function.html#The-Data-Object-In-Depth
        return {
          props: itemProps,
          attrs: itemAttrs,
          ...
        }
      }
    },
    components: { 'virtual-list': virtualList }
  }
</script>

Whenever you want to change any item data from list in this mode, you need call public method forceRender() after source data change. Increase or decrease items, you need to keep itemcount and call forceRender() together.

variable height

Using variable height, props remain and size is still required. All the index variable height and scroll offset will be cached by virtual-list after the binary-search calculate, if you want to change anyone <item/> height from data, you need call public method updateVariable(index) to clear the offset cache.

If you assign variable as true, do not set inline style height inside <item/> component, you must set inline style height on <item/> component outside directly, such as:

<template>
  <div>
    <virtual-list :size="40" :remain="8" :variable="true">
      <item v-for="item of items" :key="item.id" :style="{ height: item.height + 'px' }" />
    </virtual-list>
  </div>
</template>

More use ways or getting start you can refer to these clearly demos or test suites.

Performance comparison

According to the demos above, here are lists of approximate statistics:

Build time wasted

Build amount	item-mode	vfor-mode	without virtual list
1,000	8 ms	35 ms	220 ms
10,000	10 ms	170 ms	1500 ms
100,000	20 ms	1300 ms	Browser crash!

Total memory used

Build amount	item-mode	vfor-mode	without virtual list
1,000	10 MB	80 MB	200 MB
10,000	25 MB	120 MB	220 MB
100,000	55 MB	550 MB	Browser crash!

Attentions

• Must assign the :key property on <item> component or dom frag with v-for directive.

• Consider using box-sizing: border-box on <item> if you want absolutely correct scroll height.

Props type

Props of basic:

Prop	Type	Required	Description
size	Number	✓	Each list item height, in variable height, this prop just use to calculate the virtual-list outside container viewport fixed height.
remain	Number	✓	How many items should be shown in virtual-list viewport, so size and remain determine the outside container viewport height (size × remain).

Props of performance:

Prop	Type	Required	Description
bench	Number	*	Default value is equal to remain, unreached items count, not show in virtual-list viewport but exist in real DOM, the larger the bench, the higher the scroll performance will achieved.
debounce	Number	*	It's disabled by default, milliseconds of using debounce function to ensure scroll event doesn't fire so often that it bricks browser performance.

Props of position:

Prop	Type	Required	Description
start	Number	*	Default value is 0, the initial scroll start index. It must be integer and in the range of list index, if invalid there will be effected as 0 or the last one.
offset	Number	*	Default value is 0, the initial scroll offset. If both start and offset are assigned at initialization, start is preferred.

Props of element and class:

Prop	Type	Required	Description
rtag	String	*	Default value is div, virtual-list root element tag name, in all cases it's style is set to display: block;
wtag	String	*	Default value is div, virtual-list item wrapper element tag name, in all cases it's style is set to display: block;
wclass	String	*	Default is no classname, virtual-list item wrapper element class, if assign this prop, you better not to change it's CSS box model.
wstyle	Object	*	Default value is {}, though you can add your own styles for a child element except display and padding because they are used by the library

Props of scroll mode:

Prop	Type	Required	Description
pagemode	Boolean	*	Let virtual-list scroll with window page viewport.
scrollelement	HTMLElement	*	Let virtual-list scroll with a parent element. When pagemode is true, scrollelement is ignored.

Props of scroll event:

Prop	Type	Required	Description
totop	Function	*	Called when virtual-list is scrolled to top, no param.
tobottom	Function	*	Called when virtual-list is scrolled to bottom, no param.
onscroll	Function	*	Called when virtual-list is scrolling, with param: (event, data).

Props of variable height:

Prop	Type	Required	Description
variable	Function or Boolean	*	If assign Function, this prop is a variable height getter function which is called with param: (index) when each item is ready to be calculated; if assign Boolean, virtual-list will get each item variable height by it's inline style height automatic.

Props of item-mode:

Prop	Type	Required	Description
item	Component	*	List item vue component or vNode.
itemcount	Number	*	List total count, you should update this prop when source data changed.
itemprops	Function	*	A function call when each item is going to be rendered, you can assign props or data to each item component in this function.

Public methods

Here are some usefull public methods you can call via ref:

• forceRender(): force render virtual-list if you need or make it refresh.

• updateVariable(index): update item height by index in variable height list.

Contributions

Welcome to improve this vue component with any issue, pull request or code review!

Changelogs

Maintain and update occasionally, for changes see release.

License

MIT License