此JavaScript代码段的正确变量范围是什么

Question

I have written the function below. I need to read the dimensions of an image and then scale it back. After the initial callback I want to use the width and height values I've calculated to resize and save the image. My variables are out of scope though and I get a ReferenceError: width is not defined . How do I correctly scope these variables so they are available to the resize function?

  function saveImage(image) {
    return new Promise((resolve, reject) => {
      gm(image.data).size(function(error, value) {
        if (value.width > image.maxSize || value.height > image.maxSize) {
          max = Math.max(value.width, value.height);
          if (value.width == max) {
            width = image.maxSize; height = null;
          } else {
            height = image.maxSize; width = null;
          }
        } else {
          width = value.width; height = value.height;
        }
      })
      .resize(width, height)
      .write('./tmp/test.jpg', function(error, value) {
        if (!error) console.log(error);
      });;
    });
  }

Answer 1

您应该正确定义变量...我更喜欢您应该了解es6语法，并对变量使用“ let”和“ const”，范围很广，谢谢：-@ ravi

Answer 2

In the promise you use an arrow function, but in the .size() line below you use an old style anonymous function, and then you lose your scope. You can try using arrow function for .size()

.size((error, value) => {})