JavaScript，异步/等待和承诺

Question

I have a problem with async/await and some Promises.

I have this code. It starts here:

let valid = await LoadRouter.load(body);
console.log(valid);//showing me Pending Promises

The function is:

loadGeneratingUnits(data){
   let newUGArray = [];
   try {
     const result =  data.map(async (itemGU, index) => {
        const checGU = await this.checkDataGu(itemGU.nombre);
        if(!checGU){
           let newUG = {
              generating_unit_name: itemGU.nombre,
              description: (!itemGU.descripcion) ? null : itemGU.descripcion,
              it_generating_unit_id: (!itemGU.it_unidad_generadora) ? 0 : itemGU.it_unidad_generadora
           }
           newUGArray.push(newUG);
        }
     }) 

     return result;

   } catch (error) {
      throw new Error(error.message)

   }
}

This one is where I have the problems

async checkDataGu(guName = null){
  if(guName){
      return await generatingUnitModel.findOne({
         attributes: [
            'id',
            'generating_unit_name',
         ],
          where: {
              generating_unit_name: guName

          }
      })
  }

}

Any comment about the use of async/await on this code?

Answer 1

By making the callback to data.map() async, data.map() is now transforming the data into an array of Promises , because the return value of an async function is always a Promise. await only will wait for a Promise to resolve, not an array of them. You should use Promise.all for that:

 const result =  Promise.all(data.map(async (itemGU, index) => {
    const checGU = await this.checkDataGu(itemGU.nombre);
    if(!checGU){
       let newUG = {
          generating_unit_name: itemGU.nombre,
          description: (!itemGU.descripcion) ? null : itemGU.descripcion,
          it_generating_unit_id: (!itemGU.it_unidad_generadora) ? 0 : itemGU.it_unidad_generadora
       }
       newUGArray.push(newUG);
    }
 }))

Now result is one Promise that will resolve with an array of the values each inner Promise resolved with. Ultimately this means your upper let valid = await LoadRouter.load(body); should resolve with the array you expect.