Vue利用canvas实现移动端手写板

<template>
<div class="hello">
<!--touchstart,touchmove,touchend,touchcancel 这-->
<button type="" v-on:click="clear">清除</button>
<button v-on:click="save">保存</button>
<canvas id="canvas" width="300" height="600" style="border:1px solid black">Canvas画板</canvas>
<img v-bind:src="url" alt="">
</div>

</template>

<script>
var draw;
var preHandler = function(e){e.preventDefault();}
class Draw {
constructor(el) {
this.el = el
this.canvas = document.getElementById(this.el)
this.cxt = this.canvas.getContext('2d')
this.stage_info = canvas.getBoundingClientRect()
this.path = {
beginX: 0,
beginY: 0,
endX: 0,
endY: 0
}
}
init(btn) {
var that = this;

this.canvas.addEventListener('touchstart', function(event) {
document.addEventListener('touchstart', preHandler, false);
that.drawBegin(event)
})
this.canvas.addEventListener('touchend', function(event) {
document.addEventListener('touchend', preHandler, false);
that.drawEnd()

})
this.clear(btn)
}
drawBegin(e) {
var that = this;
window.getSelection() ? window.getSelection().removeAllRanges() : document.selection.empty()
this.cxt.strokeStyle = "#000"
this.cxt.beginPath()
this.cxt.moveTo(
e.changedTouches[0].clientX - this.stage_info.left,
e.changedTouches[0].clientY - this.stage_info.top
)
this.path.beginX = e.changedTouches[0].clientX - this.stage_info.left
this.path.beginY = e.changedTouches[0].clientY - this.stage_info.top
canvas.addEventListener("touchmove",function(){
that.drawing(event)
})
}
drawing(e) {
this.cxt.lineTo(
e.changedTouches[0].clientX - this.stage_info.left,
e.changedTouches[0].clientY - this.stage_info.top
)
this.path.endX = e.changedTouches[0].clientX - this.stage_info.left
this.path.endY = e.changedTouches[0].clientY - this.stage_info.top
this.cxt.stroke()
}
drawEnd() {
document.removeEventListener('touchstart', preHandler, false);
document.removeEventListener('touchend', preHandler, false);
document.removeEventListener('touchmove', preHandler, false);
//canvas.ontouchmove = canvas.ontouchend = null
}
clear(btn) {
this.cxt.clearRect(0, 0, 300, 600)
}
save(){
return canvas.toDataURL("image/png")
}
}

export default {
data () {
return {
msg: 'Welcome to Your Vue.js App',
val:true,
url:""
}
},
mounted() {
draw=new Draw('canvas');
draw.init();
},
methods:{
clear:function(){
draw.clear();
},
save:function(){
var data=draw.save();
this.url = data;
console.log(data)
},

　　　mutate(word) {
this.$emit("input", word);
},

} } </script> <!-- Add "scoped" attribute to limit CSS to this component only --> <style scoped> h1, h2 { font-weight: normal; } ul { list-style-type: none; padding: 0; } li { display: inline-block; margin: 0 10px; } a { color: #42b983; } #canvas { background: pink; cursor: default; } #keyword-box { margin: 10px 0; } </style>