nodejs中promise返回数据

Question

我有一个承诺的问题，我无法从该承诺返回数据...

到目前为止，我已经尝试了不同的解决方案，但我不能让它工作；我对promises还不熟悉，我正在努力理解我做错了什么：

 try {
      const classList = options.hash.class;
      const filePath = path.resolve(__dirname, path.join(PATH.documentation, options.hash.startPath, options.hash.icon + ".svg"));
      let data = fs.readFileSync(filePath, "utf-8");
      let transformedSVG;

 // Promise
      const transformable = () => {

        // another promise... apparently
        svgo.optimize(data, { path: filePath }).then(function(result) {
          transformedSVG = result.data;
          transformedSVG = transformedSVG.replace(
            /^<svg/u,
            '<svg class=" ' + classList + '" '
          );
          return transformedSVG;
        });
      };

      // wait for Promise to be finished
      async function getResult() {
        let result = transformable;
        return result;
      }
      // wait for transformable to receive data and get the result
      async function doTask() {
        return await getResult();
      }

      // store svg data returned from doTask
      transformedSVG = doTask();
      console.log(transformedSVG);
} catch (err) {
      console.error(err);
}

对此有什么帮助吗？

Answer 1

你做错了几件事。我修复了问题并添加了评论：

  const transformable = () => {
    // another promise... apparently
    return svgo.optimize(data, { path: filePath }).then(function(result) { // <== add return
      transformedSVG = result.data;
      transformedSVG = transformedSVG.replace(
        /^<svg/u,
        '<svg class=" ' + classList + '" '
      );
      return transformedSVG;
    });
  };

  // wait for Promise to be finished
  async function getResult() {
    let result = await transformable(); // <== call the function with `await`
    return result;
  }
  // wait for transformable to receive data and get the result
  async function doTask() {
    return await getResult();
  }

  // store svg data returned from doTask
  transformedSVG = await doTask(); // <== add `await`

另一件需要注意的事情是，您的doTask()方法什么也不做，因此只需删除它并直接调用await getResult()即可。