1，调用

this.getBase64(item).then((base64) => {
    console.log("图片");
})

2,方法

getBase64(img) {
  function getBase64Image(img, width, height) {
    //width、height调用时传入具体像素值，控制大小 ,不传则默认图像大小
    let canvas = document.createElement("canvas");
    canvas.width = width ? width : img.width;
    canvas.height = height ? height : img.height;
    let ctx = canvas.getContext("2d");
    ctx.drawImage(img, 0, 0, canvas.width, canvas.height);
    let dataURL = canvas.toDataURL();
    return dataURL;
  }