常用方法

hello cc

数组去重

console.log([...new Set([1, 1, 2, 2, "a", "a", "b"])]);
//[1, 2, 'a', 'b']

类型转换

let num = +"10"; // 10
let num1 = +"a"; //NaN
let bool = !!""; //false
let bool1 = !!0; //false
let bool2 = !!-1; //true
let bool3 = !![]; //true
//获取时间戳
let time = +new Date(); //Date.now()

使用===代替==

(([] == (0)[1]) == //true
  (1)[1]) === //true
  1; //false
//es6 Object.is()
NaN === NaN; //false
Object.is(1, [1]); //false
Object.is(NaN, NaN); //true

简单的随机排序

let arr = [1, 2, 3, 4, 5];
let newarr = arr.sort(() => Math.random() - 0.5); //[2, 1, 5, 3, 4]

使用 Promise 封装一个延迟器

function sleep(time) {
  return new Promise((resolve, reject) => {
    setTimeout(resolve, time);
  });
}

(async () => {
  console.time();
  await sleep(2000);
  console.timeEnd(); //这里两s后执行  //default: 2004.6728515625 ms
})();

获取文件名、文件后缀

function getFileExtName(file) {
  return file.substring(file.lastIndexOf(".") + 1);
}
function getFileName(file) {
  let sIndex = file.lastIndexOf("/") + 1 || 0;
  let eIndex = file.lastIndexOf(".");
  return file.substring(sIndex, eIndex);
}

日期格式化

function timeStrToDate(val, fmt = "yyyy-MM-dd") {
  //时间戳转日期
  let fillzero = function (n) {
    return n < 10 ? "0" + n : n;
  };
  let isValidDate = (d) => {
    return d instanceof Date && !isNaN(d.getTime());
  };
  let date = null;
  if (isValidDate(new Date(val))) {
    date = new Date(val);
  } else {
    let n = Number(val);
    if (n == NaN) return val;
    date = new Date(n);
  }
  let res = {
    "y+": date.getFullYear(),
    "M+": fillzero(date.getMonth() + 1),
    "d+": fillzero(date.getDate()),
    "h+": fillzero(date.getHours()),
    "m+": fillzero(date.getMinutes()),
    "s+": fillzero(date.getSeconds()),
  };
  for (let k in res) {
    let reg = new RegExp(k);
    if (reg.test(fmt)) {
      fmt = fmt.replace(reg, res[k]);
    }
  }
  return fmt;
}

文件转 base64

function getBase64(file) {
  return new Promise(function (resolve, reject) {
    let reader = new FileReader();
    let res = "";
    reader.readAsDataURL(file);
    reader.onload = function () {
      res = reader.result;
    };
    reader.onerror = function (error) {
      reject(error);
    };
    reader.onloadend = function () {
      resolve(res);
    };
  });
}

base64 转文件

function base642file(base64, fileName) {
  const b = Utils.dataURLtoBlob(base64);
  b.lastModifiedDate = new Date(); // 文件最后的修改日期
  b.name = fileName; // 文件名
  return new File([b], fileName, { type: b.type, lastModified: Date.now() });
}

基于 qrcode 生成带 logo 的二维码

function generateQRCode(url, config = {}, icon, fit = "contain") {
   //fit 暂未实现 用于图片的展现方式
   let imgExt = ["png", "jpg", "jpeg", "bmp", "gif"];
   if (imgExt.includes(Utils.getFileExtName(icon))) {
     let t = Date.now();
     icon = icon + `?v=${t}`;
   }
   let _config = {
     errorCorrectionLevel: "H",
     width: 300,
     height: 200,
     color: {
       dark: "#000000",
       light: "#FFFFFF",
     },
     ...config,
   };
   if (_config.widh !== _config.height) {
     let max = Math.max(_config.width, _config.height);
     _config.width = _config.height = max;
   }
   let canvas = await QRCode.toCanvas(url, _config);
   let ctx = canvas.getContext("2d");
   let scale = 0.3;
   let img = new Image();
   img.setAttribute("crossOrigin", "Anonymous");
   img.src = icon;
   return new Promise((resolve) => {
     try {
       img.onload = () => {
         ctx.fillStyle = "white";
         let rectW = _config.width * scale;
         ctx.rect(
           (_config.width - rectW) / 2,
           (_config.height - rectW) / 2,
           _config.width * scale,
           _config.height * scale
         );
         ctx.fill();
         let max = Math.max(img.width, img.height);
         const scaleFit = rectW / max;
         let w = img.width * scaleFit;
         let h = img.height * scaleFit;
         ctx.drawImage(
           img,
           (_config.width - w) / 2,
           (_config.height - h) / 2,
           w,
           h
         );
         resolve(canvas.toDataURL());
       };
     } catch (error) {
       resolve(canvas.toDataURL());
     }
   });
 }

数组分组

function groupBy(list, key) {
  return list.reduce((rv, current) => {
    (rv[current[key]] = rv[current[key]] || []).push(current);
    return rv;
  }, {});
}

groupBy(
  [
    {
      name: "Tom",
      gender: "1",
    },
    {
      name: "cc",
      gender: "1",
    },
    {
      name: "lisa",
      gender: "0",
    },
  ],
  "gender"
);
/*return
{
  0: [
    {
      name: "lisa",
      gender: "0",
    },
  ],
  1: [
    {
      name: "Tom",
      gender: "1",
    },
    {
      name: "cc",
      gender: "1",
    },
  ],
}
*/