img-lazy.js
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import { extend } from '../../vue'
import { NAME_IMG_LAZY } from '../../constants/components'
import { HAS_INTERACTION_OBSERVER_SUPPORT } from '../../constants/env'
import { MODEL_EVENT_NAME_PREFIX } from '../../constants/events'
import { PROP_TYPE_BOOLEAN, PROP_TYPE_NUMBER_STRING, PROP_TYPE_STRING } from '../../constants/props'
import { concat } from '../../utils/array'
import { requestAF } from '../../utils/dom'
import { identity } from '../../utils/identity'
import { toInteger } from '../../utils/number'
import { omit } from '../../utils/object'
import { makeProp, makePropsConfigurable, pluckProps } from '../../utils/props'
import { VBVisible } from '../../directives/visible/visible'
import { BImg, props as BImgProps } from './img'
// --- Constants ---
const MODEL_PROP_NAME_SHOW = 'show'
const MODEL_EVENT_NAME_SHOW = MODEL_EVENT_NAME_PREFIX + MODEL_PROP_NAME_SHOW
// --- Props ---
const imgProps = omit(BImgProps, ['blank'])
export const props = makePropsConfigurable(
{
...imgProps,
blankHeight: makeProp(PROP_TYPE_NUMBER_STRING),
// If `null`, a blank image is generated
blankSrc: makeProp(PROP_TYPE_STRING, null),
blankWidth: makeProp(PROP_TYPE_NUMBER_STRING),
// Distance away from viewport (in pixels)
// before being considered "visible"
offset: makeProp(PROP_TYPE_NUMBER_STRING, 360),
[MODEL_PROP_NAME_SHOW]: makeProp(PROP_TYPE_BOOLEAN, false)
},
NAME_IMG_LAZY
)
// --- Main component ---
// @vue/component
export const BImgLazy = /*#__PURE__*/ extend({
name: NAME_IMG_LAZY,
directives: {
'b-visible': VBVisible
},
props,
data() {
return {
isShown: this[MODEL_PROP_NAME_SHOW]
}
},
computed: {
computedSrc() {
const { blankSrc } = this
return !blankSrc || this.isShown ? this.src : blankSrc
},
computedBlank() {
return !(this.isShown || this.blankSrc)
},
computedWidth() {
const { width } = this
return this.isShown ? width : this.blankWidth || width
},
computedHeight() {
const { height } = this
return this.isShown ? height : this.blankHeight || height
},
computedSrcset() {
const srcset = concat(this.srcset)
.filter(identity)
.join(',')
return srcset && (!this.blankSrc || this.isShown) ? srcset : null
},
computedSizes() {
const sizes = concat(this.sizes)
.filter(identity)
.join(',')
return sizes && (!this.blankSrc || this.isShown) ? sizes : null
}
},
watch: {
[MODEL_PROP_NAME_SHOW](newValue, oldValue) {
if (newValue !== oldValue) {
// If `IntersectionObserver` support is not available, image is always shown
const visible = HAS_INTERACTION_OBSERVER_SUPPORT ? newValue : true
this.isShown = visible
// Ensure the show prop is synced (when no `IntersectionObserver`)
if (newValue !== visible) {
this.$nextTick(this.updateShowProp)
}
}
},
isShown(newValue, oldValue) {
// Update synched show prop
if (newValue !== oldValue) {
this.updateShowProp()
}
}
},
mounted() {
// If `IntersectionObserver` is not available, image is always shown
this.$nextTick(() => {
this.isShown = HAS_INTERACTION_OBSERVER_SUPPORT ? this[MODEL_PROP_NAME_SHOW] : true
})
},
methods: {
updateShowProp() {
this.$emit(MODEL_EVENT_NAME_SHOW, this.isShown)
},
doShow(visible) {
// If IntersectionObserver is not supported, the callback
// will be called with `null` rather than `true` or `false`
if ((visible || visible === null) && !this.isShown) {
// In a `requestAF()` to render the `blank` placeholder properly
// for fast loading images in some browsers (i.e. Firefox)
requestAF(() => {
this.isShown = true
})
}
}
},
render(h) {
const directives = []
if (!this.isShown) {
// We only add the visible directive if we are not shown
directives.push({
// Visible directive will silently do nothing if
// `IntersectionObserver` is not supported
name: 'b-visible',
// Value expects a callback (passed one arg of `visible` = `true` or `false`)
value: this.doShow,
modifiers: {
// Root margin from viewport
[`${toInteger(this.offset, 0)}`]: true,
// Once the image is shown, stop observing
once: true
}
})
}
return h(BImg, {
directives,
props: {
// Passthrough props
...pluckProps(imgProps, this.$props),
// Computed value props
src: this.computedSrc,
blank: this.computedBlank,
width: this.computedWidth,
height: this.computedHeight,
srcset: this.computedSrcset,
sizes: this.computedSizes
}
})
}
})