async function myfunc(fruits) {
    for (i = 0; i < 5; i  ) {
        fruits.forEach(fruitId => {
            colors = await dbHelper.getColor(fruitId);
            colors.forEach(color => {
                taste = await dbHelper.gettaste(color);
            });
        });
    }
}

How do we get this to work,with multiple for loops.The dbhelper functions are fetching some data from the database.

CodePudding user response：

Your code have a several mistakes (check out below) and should look like this:

async function myfunc(fruits) {
    try { 
        for (let i = 0; i < 5; i  ) {
            for (let fruitId of fruits) {
                colors = await dbHelper.getColor(fruitId);
                for (let color of colors) {
                    taste = await dbHelper.gettaste(color);
                }
            }
        }
    } catch(err) {
        // Handle somehow
    }
}

Why?

1. You call async methods from dbHelper inside of forEach arrow function instead of myfunc directly, so await keyword will not allowed there, you should add async keyword to methods where async methods calls.
2. Awaiting will not works there because forEach loop can't pause code execution. Solution: change forEach loops to for (... in/of ...).
3. You didn't handle errors anywhere. Keep in mind that any async method can be rejected, so you need to be ready for it and handle errors somehow. Solution: add try/catch.

Also you can check this question about asyncing during loop.

CodePudding user response：

Assuming that you want to retrieve an array of taste you can do something like this

async function myfunc(fruits) {
   const colors = await Promise.all(fruits.map(fruitId =>dbHelper.getColor(fruitId)));
   const tastes = await Promise.all(colors.map(color => dbHelper.gettaste(color)));
   ...
}

or shorter

async function myfunc(fruits) {
   const colors = await Promise.all(fruits.map(dbHelper.getColor));
   const tastes = await Promise.all(colors.map(dbHelper.gettaste));
   ...
}

CodePudding user response：

Inside forEach you define a new (arrow) function. So it will work if you use like this:

colors.forEach(async (color) => {
                taste = await dbHelper.gettaste(color);
            });

Your entire code should be:

async function myfunc(fruits) {
    for (i = 0; i < 5; i  ) {
        fruits.forEach(async (fruitId) => {
            colors = await dbHelper.getColor(fruitId);
            colors.forEach(async (color) => {
                taste = await dbHelper.gettaste(color);
            });
        });
    }
}