JavaScript Promise 返回 Pending 但我只需要值

Question

这个问题已经有答案了:

How do I return the response from an asynchronous call? (42 个回答)

已关闭 3 年前。

你能帮我解决这个代码片段吗？在这一部分中，我向我的 c# Controller 发出 ajax 请求，只是为了验证电子邮件并获取 bool 值，但在此过程中， promise 返回待处理状态会产生问题，因为我实际上只需要 promise 内的值，这里是我的代码:

let Email = input;
let valida = ValidaEmail(Email);
console.log(valida);

函数

async function ValidaEmail(email) {
    let promise = new Promise(resolve => {
        var string = JSON.stringify(email);
        var xhttp = new XMLHttpRequest();
        xhttp.open("POST", "/Home/EmailisValid", true);
        xhttp.setRequestHeader("Content-type", "application/json");
        xhttp.onreadystatechange = () => {
            if (xhttp.readyState === 4 && xhttp.status === 200)
                resolve(xhttp.response);
        };
        xhttp.send(string);
    });
    let retorno = await promise;
    console.log(retorno);
}

输出:

Answer 1

首先，您必须从 ValideEmail 返回 promise 结果。

async function ValidaEmail(email) {
    let promise = new Promise(resolve => {
        var string = JSON.stringify(email);
        var xhttp = new XMLHttpRequest();
        xhttp.open("POST", "/Home/EmailisValid", true);
        xhttp.setRequestHeader("Content-type", "application/json");
        xhttp.onreadystatechange = () => {
            if (xhttp.readyState === 4 && xhttp.status === 200)
                resolve(xhttp.response);
        };
        xhttp.send(string);
    });
    let retorno = await promise;
    console.log(retorno);
    //////
    return retorno;
    //////
}

当您使用ValidateEmail函数时，您必须使用await或.then();

let Email = input;
///
let valida = await ValidaEmail(Email);
console.log(valida);
// or
ValidaEmail(Email).then((valida) => {
   console.log(valida);
})