Javascript – Problem mit der Promise-Anwendung

Question

function loadImageAsync(url) {
  return new Promise(function(resolve, reject) {
    var image = new Image();

    image.onload = function() {
      resolve(image);
    };

    image.onerror = function() {
      reject(new Error('Could not load image at ' + url));
    };

    image.src = url;
  });
}

Was ich wissen möchte, ist, wie man diese Methode anwendet? Ich habe URL,然后再then eingegeben, um das Objektbild zu erhalten? Aber ich habe es getestet, aber es kam keine Antwort!

Answer 1

loadImageAsync('./img/news-1.png').then((img) => {
    document.getElementById("app").appendChild(img)
    console.log(img)
})

这么调用，在then的参数就是resolve的参数， 也就是image对象，把这个对象append到p上就可以实现功能

这是最终结果

这是console

Answer 2

loadImageAsync(url).then(function(img) { doSomething(); }).catch(function(err) { handleError(err); });

Answer 3

可以的 ，我在浏览器里试过了：

function loadImageAsync(url) {
  return new Promise(function(resolve, reject) {
    var image = new Image();

    image.onload = function() {
      resolve(image);
    };

    image.onerror = function() {
      reject(new Error('Could not load image at ' + url));
    };

    image.src = url;
  });
}

loadImageAsync('https://www.baidu.com/img/bd_logo1.png').then(function(){alert("jiazai wancheng")})