函数内部promise的返回值是如何工作的（第一次学习js）

发布于 2025-01-20 06:31:32 字数 678 浏览 1 评论 0原文

我最近开始学习JS，并看到了关于承诺的教程，在一项手练习期间，我尝试写自己的诺言。



function isEven(number){
    return new Promise((resolve,reject)=>{
        res = "";
        if(isNaN(number)){
            reject();
            return res;

        }
        else{ 
            if(number%2 == 0){
                res= "Even";
            }
            res = "odd";
            resolve();
            return res;
        }
    })
}
var num = 45
let str = isEven(num).then(()=>{
    console.log("succesfull");
}).catch(()=>{
    console.log("NAN");
})
document.getElementById('number').innerHTML = str;

我得到的响应[Object Promise]。我想访问通过函数返回的str值，请有人帮助我理解这个概念

原文

I recently started learning JS and saw a tutorial on promises, and during a handson exercise i tried writing my own promise.



function isEven(number){
    return new Promise((resolve,reject)=>{
        res = "";
        if(isNaN(number)){
            reject();
            return res;

        }
        else{ 
            if(number%2 == 0){
                res= "Even";
            }
            res = "odd";
            resolve();
            return res;
        }
    })
}
var num = 45
let str = isEven(num).then(()=>{
    console.log("succesfull");
}).catch(()=>{
    console.log("NAN");
})
document.getElementById('number').innerHTML = str;

and the response i got [object Promise] . I want to access the str value which is returned through function isEven , kindly someone help me to understand this concept

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旧故 2025-01-27 06:31:32

您的问题是，当您在某些条件下解决/拒绝承诺时，没有与该操作相关的值。您需要将您想要获取的任何内容传递给这些方法，如下所示：

function isEven(number){
    return new Promise((resolve,reject)=>{
        res = "";
        if(isNaN(number)){
            reject(res)
        }
        else{ 
            if(number%2 == 0){
                res= "Even";
            }
            res = "odd";
            resolve(res)
        }
    })
}
var num = 45
let str = isEven(num).then(()=>{
    console.log("succesfull");
}).catch(()=>{
    console.log("NAN");
})
document.getElementById('number').innerHTML = str;

如果您在 Promise 上使用 .then ，它会自动假设所述 Promise 将解析，并将解析后的值作为任何回调函数的输入你放进去

Your problem is that, while you're resolving/rejecting the promise under certain conditions, there are no values associated with that action. You need to pass whatever you want to grab to those methods as below:

function isEven(number){
    return new Promise((resolve,reject)=>{
        res = "";
        if(isNaN(number)){
            reject(res)
        }
        else{ 
            if(number%2 == 0){
                res= "Even";
            }
            res = "odd";
            resolve(res)
        }
    })
}
var num = 45
let str = isEven(num).then(()=>{
    console.log("succesfull");
}).catch(()=>{
    console.log("NAN");
})
document.getElementById('number').innerHTML = str;

If you use the .then on a Promise it auto assumes that said Promise will resolve, taking that resolved value as input for whatever callback function you're putting inside

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