0 == false // true 
0 === false // false 
2 == "2" // true 
2 === "2" // false 

// example 
const val = "123"; 
if (val === 123) { 
  console.log(val); 
  // it cannot not be reached 
} 
if (val === "123") { 
  console.log(val); 
  // it can be reached
}

// 不推荐
let daysSLV = 10;
let y = new Date().getFullYear();
let ok;
if (user.age > 30) {
  ok = true;
}

//  推荐
const MAX_AGE = 30;
let daysSinceLastVisit = 10;
let currentYear = new Date().getFullYear();
...
const isUserOlderThanAllowed = user.age > MAX_AGE;

// 不要添加一些额外且不必要的词汇到你的变量名称中。

let nameValue;
let theProduct;

// 推荐
let name; 
let product;

function Person(name) {
  this.name = name;
}  


function Student(name) {  
  Person.call(this, name);
}

Student.prototype = Object.create(Person.prototype);
//  Student 的原型会被设置为 Person。

// 实际上想要将 Student 的原型设置为 Student。
// 需要这么写
Student.prototype.constructor = Student;

// 或者
class Student extends Person {
}

<script id="worker" type="javascript/worker">
  self.onmessage = (e) => {
    self.postMessage('msg');
  };
</script>
<script>
  const blob = new Blob([
    document.querySelector('#worker').textContent
  ]);

  const worker = new Worker(window.URL.createObjectURL(blob));
  worker.onmessage = (e) => {
    console.log(e.data);
  }
  worker.postMessage("hello");
</script>

//  不要这么写
['1','2','3'].map(parseInt)

// 可以
['1','2','3'].map(Number)
['1','2','3'].map(num => parseInt(num, 10))

// 当 x === 1 返回 false 不想调用 doSomethingElse 时
x === 1 ? doSomething() : doSomethingElse();

// 可以
x === 1 && doSomething();

yarn cache clear

const el = document.getElementById('foo');
el.textContent = 'foo';

const tool = {
  //base64转file
  dataURLtoFile (dataurl, filename) {
    let arr = dataurl.split(','), mime = arr[0].match(/:(.*?);/)[1],
      bstr = atob(arr[1]), n = bstr.length, u8arr = new Uint8Array(n)
    while (n--) {
      u8arr[n] = bstr.charCodeAt(n)
    }
    return new File([u8arr], filename, {type: mime})
  },

  // 压缩图片
  compress (img) {
    let originWidth = img.width, // 压缩后的宽
      originHeight = img.height,
      maxWidth = 600, maxHeight = 600,
      quality = 0.8, // 压缩质量
      canvas = document.createElement('canvas'),
      drawer = canvas.getContext('2d');
    // 目标尺寸
    let targetWidth = originWidth,
      targetHeight = originHeight
    // 图片尺寸超过300x300的限制
    if (originWidth > maxWidth || originHeight > maxHeight) {
      if (originWidth / originHeight > maxWidth / maxHeight) {
        // 更宽，按照宽度限定尺寸
        targetWidth = maxWidth
        targetHeight = Math.round(maxWidth * (originHeight / originWidth))
      } else {
        targetHeight = maxHeight
        targetWidth = Math.round(maxHeight * (originWidth / originHeight))
      }
    }
    canvas.width = targetWidth
    canvas.height = targetHeight
    drawer.clearRect(0, 0, canvas.width, canvas.height)
    drawer.drawImage(img, 0, 0, canvas.width, canvas.height)
    let base64 = canvas.toDataURL('image/jpeg', quality) // 压缩后的base64图片
    let file = this.dataURLtoFile(base64, Date.parse(Date()) + '.jpg')
    file = {content: base64, file: file}
    console.log(file)//压缩后的file
    return file
  },
}
export default tool

1. 可以直接把base64数据转为File对象，如下：
// dataUrl数据转为File对象，dataUrl表示图片的base64数据
dataURLtoFile (dataurl, filename) {
var arr = dataurl.split(',')
var mime = arr[0].match(/:(.*?);/)[1]
var bstr = atob(arr[1])
var n = bstr.length; var u8arr = new Uint8Array(n)
while (n--) {
u8arr[n] = bstr.charCodeAt(n)
}
return new File([u8arr], filename, { type: mime })
}
2. 或者你想把上文 方法返回的blob对象转为File对象，可以这样写：
/**
 * Blob对象转为File对象
 * @param {object} blob 二进制对象
 * @param {string} fileName 文件名称
 * @return {object} blob改造后的file文件对象。
 * 注意：file对象就是一个特殊的blob对象
 */
function blobToFile(blob, fileName){
  blob.lastModifiedDate =new Date();
  blob.name = fileName;
  return blob;
}