如何从异步调用返回响应

Question

function foo() {
    var result;

    $.ajax({
        url: '...',
        success: function(response) {
            result = response;
            // return response; // <- I tried that one as well
        }
    });

    return result; // It always returns `undefined`
}

function foo() {
    var result;

    fs.readFile("path/to/file", function(err, data) {
        result = data;
        // return data; // <- I tried that one as well
    });

    return result; // It always returns `undefined`
}

使用promise的then块的示例：

function foo() {
    var result;

    fetch(url).then(function(response) {
        result = response;
        // return response; // <- I tried that one as well
    });

    return result; // It always returns `undefined`
}

Answer 1

使用ES2017时，您应该将此作为函数声明。

async function foo() {
  var response = await $.ajax({url: '...'})
  return response;
}

并像这样执行它。

(async function() {
  try {
    var result = await foo()
    console.log(result)
  } catch (e) {}
})()

或者Promise语法。

foo().then(response => {
  console.log(response)

}).catch(error => {
  console.log(error)

})

// The function declaration:
async function foo() {
  var response = await $.ajax({
    url: 'https://jsonplaceholder.typicode.com/todos/1'
  })
  return response;
}

// Execute it like this:
(async function() {
  try {
    var result = await foo()
    console.log(result)
  } catch (e) {}
})()

// Or use Promise syntax:
foo().then(response => {
  console.log(response)
}).catch(error => {
  console.log(error)
})

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