何时或谁将解析和拒绝函数传递给 JS 承诺? [英] When or who does pass resolve and reject functions to JS promises?

问题描述

我已经开始学习 javascript 承诺.但我就是无法理解承诺的概念.最让我烦恼的是，谁将 Resolver 和 Reject 函数传递给 promise 构造函数?

I have begin learning javascript promises. But I just can't understand the concept of promises. The thing that bothers me most is who is passing the Resolver and Reject function to a promise constructor ?

请看这个 Promise 示例:

See this example of Promise:

function getImage(url){
    return new Promise(function(resolve, reject){
        var img = new Image()
        img.onload = function(){
            resolve(url)
        }
        img.onerror = function(){
            reject(url)
        }
        img.src = url
    })
}

现在谁传递了res​​olve和reject方法，因为我对javascript的理解告诉我这个脚本会抛出未知变量错误，因为resolve和rejects没有定义?

Now who does pass resolve and reject methods , as my understanding of javascript says me that this script will throw unknown variable errors as resolve and rejects are not defined ?

getImage('doggy.jpg').then(function(successurl){
    document.getElementById('doggyplayground').innerHTML = '<img src="' + successurl + '" />'
}).catch(function(errorurl){
    console.log('Error loading ' + errorurl)
})

现在你看到了一个类似上面的方法，传递这些方法(解析和拒绝)的唯一方法是通过 then 和 catch ，如上面对 getImage 的方法调用所使用的那样.

Now you see a method like the above , the only way these methods(resolve and reject) are passed are via then and catch as used in above method call to getImage.

推荐答案

最让我烦恼的是谁将 Resolver 和 Reject 函数传递给 promise 构造函数?

The thing that bothers me most is who is passing the Resolver and Reject function to a promise constructor ?

没人.

函数由promise构造函数传递.

The functions are passed by the promise constructor.

它们被传递给作为第一个参数传递给promise构造函数的函数.

They are passed to the function which you pass as the first argument to the promise constructor.

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