我涉足html5和javascript（两者我一无所知）。我找到了一些html5的示例，将其复制并开始尝试。这是一些代码。这个想法是，当按下任何键时，两个正方形开始向左移动（尚未清除在其后面）。我不明白的是为什么我不能更改颜色（下面已指出）。有任何想法吗？我显然做错了什么。
<!doctype html>
<!-- this source copied from http://www.xanthir.com/blog/b48B0 -->
<canvas width=800 height=800>
</canvas>
<script>
var canvas = document.getElementsByTagName("canvas")[0];
var context = canvas.getContext('2d');
var x = 230;
var y = 380;
// First, we'll paint the whole canvas black.
context.fillStyle = "black";
context.fillRect(0,0,800,800);
context.fillStyle = "red";
context.fillRect(0,0,30,30);
context.fillRect(0,100,30,30);
context.fillStyle = "green";
context.fillRect(0,200,30,30);
// Now we'll draw some shapes
// circle
context.fillStyle = "#06c";
context.strokeStyle = "white";
// These can be any CSS color.
context.lineWidth = 3;
context.beginPath();
context.moveTo(450,250);
context.arc(375,250,75,0,2*Math.PI,false)
context.closePath();
context.fill();
context.stroke();
// A triangle! And a rainbow!
context.beginPath();
context.moveTo(150,50);
context.lineTo(90,150);
context.lineTo(210,150);
context.lineTo(150,50);
context.closePath();
var rainbow = context.createLinearGradient(150,50,150,150);
rainbow.addColorStop(.1,"red");
rainbow.addColorStop(.3,"orange");
rainbow.addColorStop(.5,"yellow");
rainbow.addColorStop(.7,"lime");
rainbow.addColorStop(.9,"blue");
context.fillStyle = rainbow;
context.fill();
// Some text! And a shadow!
context.shadowOffsetX = -2;
context.shadowOffsetY = 2;
context.shadowColor = "#f88";
context.shadowBlur = .01;
context.fillStyle = "red";
context.font = "bold 72px monospace";
context.fillText("Foo Bar",30,400);
context.fillStyle = "blue";
context.fillRect(0,300,30,30);
// ???????????? end of main. The current context now seems to remain (blue fillstyle with some shadow )
// routine here : press any key to animate two new blocks over writing ----------------
document.onkeydown = function(e) {
context.fillstyle = "red"; // <-- ???????? this doesnt work (remains same colour as last one in main )
context.fillRect(x,y,50,50); // <-- ???????? draws a square in blue, not red
x = x - 5;
context.fillstyle = "white"; // <-- ???????? this doesnt work (remains same colour as last one in main )
context.fillRect(x -100,y ,50,50); // <-- ???????? draws a square in blue, not white
}
最佳答案
因为您写的是fillstyle而不是fillStyle。您需要大写S。
它在Javascript中有效，因为您只是将新的fillstyle字段（不存在且没有意义）附加到该上下文。
所以你要小心。打字错误可能会造成很多麻烦，因为从技术上讲，生成的代码不是错误，但肯定不是您想要的！