https://juejin.im/post/5edb2d1ef265da7717203113#heading-3
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width">
<title>JS Bin</title>
<style>
body {
}
#button {
border: 1px solid pink;
width: 100px;
}
#canvas {
border: 1px solid;
}
</style>
</head>
<body>
<div id="button">画笔
</div>
<canvas id="canvas"></canvas>
</body>
<script>
let canvas = document.getElementById('canvas')
let ctx = canvas.getContext('2d')
let isPress = false
let isDraw = true
let button = document.getElementById('button')
button.addEventListener('click', function(){
if(button.textContent === '画笔'){
button.textContent = '橡皮'
isDraw = false
} else {
button.textContent = '画笔'
isDraw = true
}
})
canvas.addEventListener('mousedown', function(){
isPress = true
if(isDraw) {
ctx.beginPath()
}
})
canvas.addEventListener('mousemove', function(e){
let x = e.offsetX
let y = e.offsetY
if(isPress) {
if(isDraw) {
ctx.lineTo(x, y)
ctx.stroke()
}else {
ctx.clearRect(x-20, y-20, 20, 20)
}
}
})
canvas.addEventListener('mouseup', function(){
isPress = false
})
</script>
</html>
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