const subStringToImage = (params) => {
            const { str = '',color = '#FFF',background = '#4F54FF',size = 60,fontSize = 
            20  } = params
            if(str.length < 0) return console.error('字符不能为空!')
            const text = str.slice(0, 1)
            const canvas = document.createElement('canvas')
            const ctx = canvas.getContext('2d')
            canvas.width = size
            canvas.height = size
            const x = canvas.width / 2;
            const y = canvas.height / 2;
            const radius = size/2;
            ctx.fillStyle = background;
            ctx.arc(x, y, radius, 0, 2 * Math.PI);
            ctx.fill();
            ctx.font = `${fontSize}px Arial`;
            ctx.textAlign = 'center'
            ctx.textBaseline = 'middle'
            ctx.fillStyle = color
            ctx.fillText(text,size/2,size/2);
            const url = canvas.toDataURL('iamge/png')
            const image = new Image()
            image.src = url
            document.body.appendChild(image)
        }
        subStringToImage({ str:'仙古梦回' })

示例：