JS 缩小图片

 getBase64Image(imgpath:string) { 
    var img = new Image(); //新建一个图片对象
    img.src = imgpath;

    let canvas = document.createElement("canvas"); 
    
    let w=img.width;
    let h=img.height;

    if(h>w) {
      h=1024;
      w=w*h/img.height;
    }else{
      w=1024;
      h=w*h/img.width;
    }

    canvas.width = w;
    canvas.height = h; 
    const ctx = canvas.getContext("2d"); 


    ctx?.drawImage(img, 0, 0, w, h); 
    var ext = img.src.substring(img.src.lastIndexOf(".")+1).toLowerCase(); 
    var dataURL = canvas.toDataURL("image/"+ext); 
    this.src=dataURL;
    console.log(dataURL);
    return dataURL; 
}