改变图片大小的js

function resizeImage(file, maxWidth, maxHeight, callback) {
    let img = new Image();
    img.src = URL.createObjectURL(file);
    img.onload = function() {
        let width = img.width;
        let height = img.height;

        // 计算新的尺寸
        if (width > height) {
            if (width > maxWidth) {
                height *= maxWidth / width;
                width = maxWidth;
            }
        } else {
            if (height > maxHeight) {
                width *= maxHeight / height;
                height = maxHeight;
            }
        }

        let canvas = document.createElement('canvas');
        canvas.width = width;
        canvas.height = height;
        let ctx = canvas.getContext('2d');
        ctx.drawImage(img, 0, 0, width, height);

        // 将调整后的图片转换为DataURL
        let dataUrl = canvas.toDataURL('image/jpeg');
        callback(dataUrl);
    };
}

// 使用示例
let input = document.querySelector('input[type=file]');
input.addEventListener('change', function(event) {
    let file = event.target.files[0];
    resizeImage(file, 300, 300, function(resizedImageUrl) {
        // 在这里使用调整后的图片URL
        console.log(resizedImageUrl);
    });
});