异步函数在 map function 内没有以正确的顺序执行

Question

I have created an async function that will extra the data from the argument, create a Postgres query based on a data, then did some processing using the retrieved query data. Yet, when I call this function inside a map function, it seemed like it has looped through all the element to extra the data from the argument first before it proceed to the second and the third part, which lead to wrong computation on the second element and onwards(the first element is always correct). I am new to async function, can someone please take at the below code? Thanks!

async function testWeightedScore(test, examData) {
    var grade = [];
    const testID = examData[test.name];
    console.log(testID);
    var res = await DefaultPostgresPool().query(
         //postgres query based on the score constant
        );
    var result = res.rows;
    for (var i = 0; i < result.length; i++) {
        const score = result[i].score;
        var weightScore = score * 20;
        //more computation
        const mid = { "testID": testID, "score": weightScore, more values...}; 
        grade.push(mid);
    }
    return grade;
}

(async () => {
    const examSession = [{"name": "Sally"},{"name": "Bob"},{"name": "Steph"}]
    const examData = {
        "Sally": 384258,
        "Bob": 718239,
        "Steph": 349285,
    };
    var test = [];

    examSession.map(async sesion => {
        var result = await testWeightedScore(sesion,examData); 
        let counts = result.reduce((prev, curr) => {
            let count = prev.get(curr.testID) || 0;
            prev.set(curr.testID, curr.score + count);
            return prev;
          }, new Map());
        let reducedObjArr = [...counts].map(([testID, score]) => {
            return {testID, score}
        })      
        console.info(reducedObjArr);
    }
    );
})();

// The console log printed out all the tokenID first(loop through all the element in examSession ), before it printed out reducedObjArr for each element

Answer 1

The async/await behaviour is that the code pause at await, and do something else (async) until the result of await is provided.

So your code will launch a testWeightedScore , leave at the postgresql query (second await ) and in the meantime go to the other entries in your map , log the id, then leave again at the query level. I didn't read your function in detail however so I am unsure if your function is properly isolated or the order and completion of each call is important.

If you want each test to be fully done one after the other and not in 'parallel', you should do a for loop instead of a map .