Typescript map 不等待结果[重复]

Question

:

How to return many Promises and wait for them all before doing other stuff (6 answers)

Closed 7 months ago .

I'm using a many to many relation with TypeOrm who is needing Ids to find the subcategories of an article.

The problem is that the map is not awaiting to push the result in the array.

Here is my map function with the list and the logs:

const subcategories = articleDto.subcategoriesIds.split(',').map(x => +x)
const subcategoriesList = []
    
await subcategories.map(async (subcategoryId) => {
    console.log('start:' + subcategoryId)
    const category = await this.subcategoriesService.getSubcategoryById(subcategoryId);
    console.log('mid:' + subcategoryId)
    await subcategoriesList.push(category);
    console.log('end:' + subcategoryId)
});

console.log('### ' + subcategories);
console.log('### ' + subcategoriesList);

Here is the output of the logs:

start:2
start:3
### 2,3
### 
mid:2
end:2
mid:3
end:3

I'm not understanding why the result is not awaited, thanks for the help if you know how to manage with this problem.

EDIT: Solved this issue by adding a Promise.all using map inside

const subcategories = articleDto.subcategoriesIds.split(',').map(x => +x);

const subcategoriesList = await Promise.all(subcategories.map((subcategoryId) => {
      return new Promise((resolve => {
        this.subcategoriesService.getSubcategoryById(subcategoryId).then(result => {
          resolve(result);
        });
      }))
    }));

Answer 1

Array prototype methods don't await even if they are async. The code fires in a synchronous manner still. If you need these to await you can do

const subcategories = articleDto.subcategoriesIds.split(',').map(x => +x)
const subcategoriesList = []

for (const subCategoryId of subcategories) {
  console.log('start:' + subcategoryId)
  const category = await this.subcategoriesService.getSubcategoryById(subcategoryId);
  console.log('mid:' + subcategoryId)
  await subcategoriesList.push(category);
  console.log('end:' + subcategoryId);
}

console.log('### ' + subcategories);
console.log('### ' + subcategoriesList);