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index.js
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(function (root, factory) {
var namespace = 'VirtualScrollList'
if (typeof exports === 'object' && typeof module === 'object') {
module.exports = factory(namespace, require('vue'))
} else if (typeof define === 'function' && define.amd) {
define(['vue'], factory.bind(root, namespace))
} else if (typeof exports === 'object') {
exports[namespace] = factory(namespace, require('vue'))
} else {
root[namespace] = factory(namespace, root['Vue'])
}
})(this, function (namespace, Vue2) {
if (typeof Vue2 === 'object' && typeof Vue2.default === 'function') {
Vue2 = Vue2.default
}
var _debounce = function (func, wait, immediate) {
var timeout
return function () {
var context = this
var args = arguments
var later = function () {
timeout = null
if (!immediate) {
func.apply(context, args)
}
}
var callNow = immediate && !timeout
clearTimeout(timeout)
timeout = setTimeout(later, wait)
if (callNow) {
func.apply(context, args)
}
}
}
return Vue2.component(namespace, {
props: {
size: { type: Number, required: true },
remain: { type: Number, required: true },
rtag: { type: String, default: 'div' },
wtag: { type: String, default: 'div' },
wclass: { type: String, default: '' },
start: { type: Number, default: 0 },
offset: { type: Number, default: 0 },
variable: [Function, Boolean],
bench: Number,
debounce: Number,
totop: Function,
tobottom: Function,
onscroll: Function,
item: { type: Object },
itemcount: { type: Number },
itemprops: { type: Function }
},
created: function () {
var start = this.start >= this.remain ? this.start : 0
var keeps = this.remain + (this.bench || this.remain)
this.delta = {
start: start, // start index.
end: start + keeps - 1, // end index.
keeps: keeps, // nums keeping in real dom.
total: 0, // all items count, update in filter.
offsetAll: 0, // cache all the scrollable offset.
paddingTop: 0, // container wrapper real padding-top.
paddingBottom: 0, // container wrapper real padding-bottom.
varCache: {}, // object to cache variable index height and scroll offset.
varAverSize: 0, // average/estimate item height before variable be calculated.
varLastCalcIndex: 0 // last calculated variable height/offset index, always increase.
}
},
watch: {
size: function () {
this.alter = 'size'
},
remain: function () {
this.alter = 'remain'
},
bench: function () {
this.alter = 'bench'
this.itemModeForceRender()
},
start: function () {
this.alter = 'start'
this.itemModeForceRender()
},
offset: function () {
this.alter = 'offset'
this.itemModeForceRender()
},
itemcount: function () {
this.alter = 'itemcount'
this.itemModeForceRender()
}
},
methods: {
onScroll: function (e) {
var delta = this.delta
var vsl = this.$refs.vsl
var offset = (vsl && (vsl instanceof Vue2 ? vsl.$el : vsl).scrollTop) || 0
if (delta.total > delta.keeps) {
this.updateZone(offset)
} else {
delta.end = delta.total - 1
}
var offsetAll = delta.offsetAll
if (this.onscroll) {
this.onscroll(e, {
offset: offset,
offsetAll: offsetAll,
start: delta.start,
end: delta.end
})
}
if (!offset && delta.total) {
this.triggerEvent('totop')
}
if (offset >= offsetAll) {
this.triggerEvent('tobottom')
}
},
// update render zone by scroll offset.
updateZone: function (offset) {
var overs = this.variable
? this.getVarOvers(offset)
: Math.floor(offset / this.size)
var delta = this.delta
var zone = this.getZone(overs)
var bench = this.bench || this.remain
// for better performance, if scroll pass items within now bench, do not update.
if (!zone.isLast && (overs > delta.start) && (overs - delta.start <= bench)) {
return
}
// we'd better make sure calls as less as possible.
if (zone.start !== delta.start || zone.end !== delta.end) {
delta.end = zone.end
delta.start = zone.start
this.forceRender()
}
},
// public method, force render ui list if we needed.
// call this before the next repaint to get better performance.
forceRender: function () {
var that = this
window.requestAnimationFrame(function () {
that.$forceUpdate()
})
},
// force render ui if using item mode.
itemModeForceRender: function () {
if (this.item) {
this.forceRender()
}
},
// return the scroll passed items count in variable.
getVarOvers: function (offset) {
var low = 0
var middle = 0
var middleOffset = 0
var delta = this.delta
var high = delta.total
while (low <= high) {
middle = low + Math.floor((high - low) / 2)
middleOffset = this.getVarOffset(middle)
// calculate the average variable height at first binary search.
if (!delta.varAverSize) {
delta.varAverSize = Math.floor(middleOffset / middle)
}
if (middleOffset === offset) {
return middle
} else if (middleOffset < offset) {
low = middle + 1
} else if (middleOffset > offset) {
high = middle - 1
}
}
return low > 0 ? --low : 0
},
// return a variable scroll offset from given index.
getVarOffset: function (index, nocache) {
var delta = this.delta
var cache = delta.varCache[index]
if (!nocache && cache) {
return cache.offset
}
var offset = 0
for (var i = 0; i < index; i++) {
var size = this.getVarSize(i, nocache)
delta.varCache[i] = {
size: size,
offset: offset
}
offset += size
}
delta.varLastCalcIndex = Math.max(delta.varLastCalcIndex, index - 1)
delta.varLastCalcIndex = Math.min(delta.varLastCalcIndex, delta.total - 1)
return offset
},
// return a variable size (height) from given index.
getVarSize: function (index, nocache) {
var cache = this.delta.varCache[index]
if (!nocache && cache) {
return cache.size
}
if (typeof this.variable === 'function') {
return this.variable(index) || 0
} else {
// when using item, it can only get current components height,
// need to be enhanced, or consider using variable-function instead
var slot = this.item
? (this.$children[index] ? this.$children[index].$vnode : null)
: this.$slots.default[index]
var style = slot && slot.data && slot.data.style
if (style && style.height) {
var shm = style.height.match(/^(.*)px$/)
return (shm && +shm[1]) || 0
}
}
return 0
},
// return the variable paddingTop base current zone.
// @todo: if set a large `start` before variable was calculated,
// here will also case too much offset calculate when list is very large,
// consider use estimate paddingTop in this case just like `getVarPaddingBottom`.
getVarPaddingTop: function () {
return this.getVarOffset(this.delta.start)
},
// return the variable paddingBottom base current zone.
getVarPaddingBottom: function () {
var delta = this.delta
var last = delta.total - 1
if (delta.total - delta.end <= delta.keeps || delta.varLastCalcIndex === last) {
return this.getVarOffset(last) - this.getVarOffset(delta.end)
} else {
// if unreached last zone or uncalculate real behind offset
// return the estimate paddingBottom avoid too much calculate.
return (delta.total - delta.end) * (delta.varAverSize || this.size)
}
},
// retun the variable all heights use to judge reach bottom.
getVarAllHeight: function () {
var delta = this.delta
if (delta.total - delta.end <= delta.keeps || delta.varLastCalcIndex === delta.total - 1) {
return this.getVarOffset(delta.total)
} else {
return this.getVarOffset(delta.start) + (delta.total - delta.end) * (delta.varAverSize || this.size)
}
},
// public method, allow the parent update variable by index.
updateVariable: function (index) {
// clear/update all the offfsets and heights ahead of index.
this.getVarOffset(index, true)
},
// return the right zone info base on `start/index`.
getZone: function (index) {
var start, end
var delta = this.delta
index = parseInt(index, 10)
index = Math.max(0, index)
var lastStart = delta.total - delta.keeps
var isLast = (index <= delta.total && index >= lastStart) || (index > delta.total)
if (isLast) {
end = delta.total - 1
start = Math.max(0, lastStart)
} else {
start = index
end = start + delta.keeps - 1
}
return {
end: end,
start: start,
isLast: isLast
}
},
// trigger a props event on parent.
triggerEvent: function (event) {
if (this[event]) {
this[event]()
}
},
// set manual scroll top.
setScrollTop: function (scrollTop) {
var vsl = this.$refs.vsl
if (vsl) {
(vsl instanceof Vue2 ? vsl.$el : vsl).scrollTop = scrollTop
}
},
// filter the shown items base on `start` and `end`.
filter: function () {
var delta = this.delta
var slots = this.$slots.default
// item mode shoud judge from items prop.
if (this.item) {
delta.total = this.itemcount
} else {
if (!slots) {
slots = []
delta.start = 0
}
delta.total = slots.length
}
var paddingTop, paddingBottom, allHeight
var hasPadding = delta.total > delta.keeps
if (this.variable) {
allHeight = this.getVarAllHeight()
paddingTop = hasPadding ? this.getVarPaddingTop() : 0
paddingBottom = hasPadding ? this.getVarPaddingBottom() : 0
} else {
allHeight = this.size * delta.total
paddingTop = this.size * (hasPadding ? delta.start : 0)
paddingBottom = this.size * (hasPadding ? delta.total - delta.keeps : 0) - paddingTop
}
if (paddingBottom < this.size) {
paddingBottom = 0
}
delta.paddingTop = paddingTop
delta.paddingBottom = paddingBottom
delta.offsetAll = allHeight - this.size * this.remain
// here we shoud try getZone to ensure start/end is right after new list. #88
var zone = this.getZone(delta.start)
if (zone.start !== delta.start || zone.end !== delta.end) {
delta.end = zone.end
delta.start = zone.start
}
var targets = []
for (var i = delta.start; i <= Math.ceil(delta.end); i++) {
// create vnode, using custom attrs binder.
var slot = this.item && this.itemprops
? this.$createElement(this.item, this.itemprops(i))
: slots[i]
targets.push(slot)
}
return targets
}
},
mounted: function () {
if (this.start) {
var start = this.getZone(this.start).start
this.setScrollTop(this.variable ? this.getVarOffset(start) : start * this.size)
} else if (this.offset) {
this.setScrollTop(this.offset)
}
},
// check if delta should update when prorps change.
beforeUpdate: function () {
var delta = this.delta
delta.keeps = this.remain + (this.bench || this.remain)
var calcstart = this.alter === 'start' ? this.start : delta.start
var zone = this.getZone(calcstart)
// if start, size or offset change, update scroll position.
if (this.alter && ~['start', 'size', 'offset'].indexOf(this.alter)) {
var scrollTop = this.alter === 'offset'
? this.offset : this.variable
? this.getVarOffset(zone.isLast ? delta.total : zone.start)
: zone.isLast && (delta.total - calcstart <= this.remain)
? delta.total * this.size : calcstart * this.size
this.$nextTick(this.setScrollTop.bind(this, scrollTop))
}
// if points out difference, force update once again.
if (calcstart !== zone.start || delta.end !== zone.end || this.alter) {
this.alter = ''
delta.end = zone.end
delta.start = zone.start
this.forceRender()
}
},
render: function (h) {
var list = this.filter()
var delta = this.delta
var dbc = this.debounce
return h(this.rtag, {
'ref': 'vsl',
'style': {
'display': 'block',
'overflow-y': 'auto',
'height': this.size * this.remain + 'px'
},
'on': {
'&scroll': dbc ? _debounce(this.onScroll.bind(this), dbc) : this.onScroll
}
}, [
h(this.wtag, {
'style': {
'display': 'block',
'padding-top': delta.paddingTop + 'px',
'padding-bottom': delta.paddingBottom + 'px'
},
'class': this.wclass
}, list)
])
}
})
})