js定义图片大小代码

<img src="example.jpg" width="300" height="200">

img {
  max-width: 100%;
  height: auto;
}

var img = new Image();
img.src = 'example.jpg';

img.onload = function() {
  // 根据实际大小调整容器大小
  var container = document.getElementById('imageContainer');
  container.style.width = img.width + 'px';
  container.style.height = img.height + 'px';
};

function resizeImageToFit(imgElement, containerElement) {
  imgElement.onload = function() {
    var containerWidth = containerElement.clientWidth;
    var containerHeight = containerElement.clientHeight;
    var imgWidth = imgElement.naturalWidth;
    var imgHeight = imgElement.naturalHeight;

    var widthRatio = containerWidth / imgWidth;
    var heightRatio = containerHeight / imgHeight;
    var ratio = Math.min(widthRatio, heightRatio);

    imgElement.style.width = (imgWidth * ratio) + 'px';
    imgElement.style.height = (imgHeight * ratio) + 'px';
  };
}

var img = document.getElementById('myImage');
var container = document.getElementById('imageContainer');
resizeImageToFit(img, container);