7820380e
 “wangming”
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<template>
<transition name="el-fade-in">
<div
v-if="visible"
@click.stop="handleClick"
:style="{
'right': styleRight,
'bottom': styleBottom
}"
class="el-backtop">
<slot>
<el-icon name="caret-top"></el-icon>
</slot>
</div>
</transition>
</template>
<script>
import throttle from 'throttle-debounce/throttle';
const cubic = value => Math.pow(value, 3);
const easeInOutCubic = value => value < 0.5
? cubic(value * 2) / 2
: 1 - cubic((1 - value) * 2) / 2;
export default {
name: 'ElBacktop',
props: {
visibilityHeight: {
type: Number,
default: 200
},
target: [String],
right: {
type: Number,
default: 40
},
bottom: {
type: Number,
default: 40
}
},
data() {
return {
el: null,
container: null,
visible: false
};
},
computed: {
styleBottom() {
return `${this.bottom}px`;
},
styleRight() {
return `${this.right}px`;
}
},
mounted() {
this.init();
this.throttledScrollHandler = throttle(300, this.onScroll);
this.container.addEventListener('scroll', this.throttledScrollHandler);
},
methods: {
init() {
this.container = document;
this.el = document.documentElement;
if (this.target) {
this.el = document.querySelector(this.target);
if (!this.el) {
throw new Error(`target is not existed: ${this.target}`);
}
this.container = this.el;
}
},
onScroll() {
const scrollTop = this.el.scrollTop;
this.visible = scrollTop >= this.visibilityHeight;
},
handleClick(e) {
this.scrollToTop();
this.$emit('click', e);
},
scrollToTop() {
const el = this.el;
const beginTime = Date.now();
const beginValue = el.scrollTop;
const rAF = window.requestAnimationFrame || (func => setTimeout(func, 16));
const frameFunc = () => {
const progress = (Date.now() - beginTime) / 500;
if (progress < 1) {
el.scrollTop = beginValue * (1 - easeInOutCubic(progress));
rAF(frameFunc);
} else {
el.scrollTop = 0;
}
};
rAF(frameFunc);
}
},
beforeDestroy() {
this.container.removeEventListener('scroll', this.throttledScrollHandler);
}
};
</script>
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