var canvas = document.getElementById(‘canvas‘),    context = canvas.getContext(‘2d‘);context.lineWidth = 30;context.font = ‘24px Helvetica‘;context.fillText(‘Click anywhere to erase‘, 175, 40);context.strokeRect(75, 100, 200, 200);context.fillRect(325, 100, 200, 200);// 鼠标按下时清除整个画布context.canvas.onmousedown = function (e) {   context.clearRect(0, 0, canvas.width, canvas.height);};

var canvas = document.getElementById(‘canvas‘),    context = canvas.getContext(‘2d‘),    gradient = context.createRadialGradient(                 canvas.width/2, canvas.height, 10,                 canvas.width/2, 0, 100);gradient.addColorStop(0, ‘blue‘);gradient.addColorStop(0.25, ‘white‘);gradient.addColorStop(0.5, ‘purple‘);gradient.addColorStop(0.75, ‘red‘);gradient.addColorStop(1, ‘yellow‘);context.fillStyle = gradient;context.rect(0, 0, canvas.width, canvas.height);context.fill();