我如何在 function 中随机制作一些东西？

Question

I have a function with some images in it here:

function rain() {
    ctx.drawImage (image1, x, y, 100, 50);
    ctx.drawImage (image2, x, y, 100, 50);
    ctx.drawImage (image3, x, y, 100, 50);
    ctx.drawImage (image4, x, y, 100, 50);
}

How do I make this function randomly choose one of these images when I call it?

Answer 1

You should put your images in an array, then pick a random index of the array.

function randomImage() {
  const images = [
    image1,
    image2,
    image3,
    image4,
  ];
  // Pick an index at random from the images array. Math.rand returns
  // a random number between 0 and 1, multiplying that by the length
  // of the images array, gets a number between 0 and the length of the
  // array, and flooring it makes it into an integer.
  const randomIndex = Math.floor(Math.rand() * images.length);
  return images[randomIndex];
}

Answer 2

I think it's inconvenient to do math when I want to deal with randomness, so I use Rando.js to make stuff like this simple and readable.

 var images = ["one", "two", "three", "four"]; console.log( rando(images).value );

 <script src="https://randojs.com/1.0.0.js"></script>

If you want to use this code, all you need to know is that the script tag sources in the rando function, and you're ready to use it right away. Just put the script tag in the head of your HTML document. It's easy, but if you need to know more, you can check out examples on the website or github repo .