利用canvas原生写一个画板

    <div class="container">

        <div class="options">
            <label>画布颜色</label>
            <input id="color" type="color" value="#000">
        </div>

        <div class="options">
            <label>画笔粗细</label>
            <input id="range" type="range" value="5" min="1" max="50">
        </div>

        <div class="options">
            <button id="clear">清空画布</button>
        </div>


        <canvas width="1000" height="500"></canvas>

    </div>

*{
    padding: 0;
    margin: 0;
    user-select: none;
    box-sizing: border-box;
}
html,body{
    display: flex;
    justify-content: center;
    align-items: center;
}
.options{
    margin-top: 20px;
    align-items: center;
    margin-top: 20px;
}
.options input{
    outline: 0;
    margin-left: 20px;
}
.options button{
    outline: 0;
    border: 0;
    padding: 10px 20px;
    border-radius: 3px;
    color: #fff;
    background: #0d53ff;
    cursor: pointer;
}
canvas{
    border: 1px solid #ccc;
    margin-top: 20px;
}

<script>

    const color = document.querySelector('#color');
    const range = document.querySelector('#range');

    let colorValue = color.value;
        rangeValue = range.value;

        color.onchange = function(){
            colorValue = color.value;
        }

        range.onchange = function(){
            rangeValue = range.value;
        }

    const canvas = document.querySelector('canvas');
    const ctx = canvas.getContext('2d');
    let flag = false;

        canvas.onmousedown = function (e) {
            flag = true;
                        //DOM.getBoundC 获取元素占document的top,left,bottom,right; width/height
            const top = canvas.getBoundingClientRect().top;
            const left = canvas.getBoundingClientRect().left;
            const mouseX = e.pageX - left;
            const mouseY = e.pageY - top;

            ctx.strokeStyle = colorValue;
            ctx.lineWidth = rangeValue;
            ctx.lineCap = 'round' //圆角
            ctx.beginPath();
            ctx.moveTo(mouseX, mouseY);
            console.log("mouseX:",mouseX, 'mouseY:',mouseY);
        }

        canvas.onmousemove = function (e) {
            if(!flag)return;
            const top = canvas.getBoundingClientRect().top;
            const left = canvas.getBoundingClientRect().left;
            const mouseX = e.pageX - left;
            const mouseY = e.pageY - top;

            ctx.lineTo(mouseX, mouseY);
            ctx.stroke();
        }

        canvas.onmouseup = function () {
            flag = false;
        }

        const clear = document.querySelector('#clear');
        clear.onclick = function () {
            ctx.clearRect(0, 0, 1000, 500);
        }
</script>