JavaScript常用工具函数汇总（浏览器环境）

/**
 * file转为base64
 * @param {*} file file对象
 * @param {*} callback 
 */
export const fileToDataURL = (file, callback) => {
 let freader = new FileReader();
 freader.readAsDataURL(file);
 freader.onload = function (e) { callback(e.target.result); }
}

/**
 * blob流转换为base64
 * @param {*} blob blob对象
 * @param {*} callback 
 */
export const blobToDataURL = (blob, callback) => {
 let freader = new FileReader();
 freader.readAsDataURL(blob);
 freader.onload = function (e) { callback(e.target.result); }
}

/**
 * base64转换为blob
 * @param {*} dataurl base64
 */
export const dataURLtoBlob = (dataurl) => {
 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 Blob([u8arr], { type: mime });
}

/**
 * 将base64转换为file,IE低版本不兼容
 * @param {*} dataurl base64
 * @param {*} filename 文件名
 */
export const 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 });
}

/**
 * 图片url转化成base64
 * @param {*} url 图片url
 * @param {*} callback 
 * @param {*} outputFormat 图片格式
 */
export const imgUrlToDataURL = (url, callback, outputFormat) => {
  let canvas = document.createElement('canvas'),
    ctx = canvas.getContext('2d'),
    img = new Image;
  img.crossOrigin = 'Anonymous';
  img.src = url + "?timeStamp=" + new Date().getTime();
  img.onload = function () {
    canvas.height = img.height;
    canvas.width = img.width;
    // ctx.drawImage(img, 0, 0);
    ctx.drawImage(this, 0, 0, img.width, img.height);
    let dataURL = canvas.toDataURL(outputFormat || 'image/png');
    // callback.call(this, dataURL);
    callback && callback(dataURL)
    canvas = null;
  };
}

export function getViewportSize() {
 let w = 0;
 let h = 0;
 if (window.innerWidth) {
  w = window.innerWidth
  h = window.innerHeight
 } else if (document.body && document.body.clientWidth) {
  w = document.body.clientWidth
  h = document.body.clientHeight
 } else if (document.documentElement && document.documentElement.clientWidth) {
  w = document.documentElement.clientWidth
  h = document.documentElement.clientHeight
 }
 return { w, h }
}

const ua = window.navigator.userAgent.toLowerCase()

// 是否微信
export const isWx = () => ua.match(/MicroMessenger/i) == 'micromessenger'

// 是否ipad
export const isIpad = () => ua.indexOf('ipad') > -1

// 是否iphone
export const isIphone = () => ua.indexOf('iphone os') > -1

// 是否uc
export const isUc = () => ua.indexOf('ucweb') > -1

// 是否windows pc
export const isWindows = () => ua.indexOf('windows') > -1

// 是否android
export const isAndroid = () => ua.indexOf('android') > -1 || ua.indexOf('adr') > -1

// 是否ios
export const isIos = () => /(iphone|ipod|ipad|ios)/i.test(ua)

// 是否qq浏览器
export const isQq = () => ua.indexOf('mqqbrowser') > -1 && ua.indexOf(' qq') < 0

// 是否qq内置浏览器
export const isQQInstalled = () => ua.indexOf(' qq') > -1 && ua.indexOf('mqqbrowser') < 0

// 开启全屏
export function launchFullscreen(element) {
 element = element || document.documentElement
 if (element.requestFullscreen) {
  element.requestFullscreen()
 } else if (element.mozRequestFullScreen) {
  element.mozRequestFullScreen()
 } else if (element.msRequestFullscreen) {
  element.msRequestFullscreen()
 } else if (element.webkitRequestFullscreen) {
  element.webkitRequestFullScreen()
 }
}

// 关闭全屏
export function exitFullscreen() {
 if (document.exitFullscreen) {
  document.exitFullscreen()
 } else if (document.msExitFullscreen) {
  document.msExitFullscreen()
 } else if (document.mozCancelFullScreen) {
  document.mozCancelFullScreen()
 } else if (document.webkitExitFullscreen) {
  document.webkitExitFullscreen()
 }
}

/**
 * @param {*} number 距离页面顶部的距离
 * @param {*} time 滚动所需时间 单位ms
 */
const scrolling = (number = 0, time) => {
  if (!time) {
    document.body.scrollTop = document.documentElement.scrollTop = number;
    return number;
  }
  // 设置循环的间隔时间 值越小消耗性能越高
  const spacingTime = 20;
  // 计算循环的次数
  let spacingInex = time / spacingTime; 
  // 获取当前滚动条位置
  let nowTop = document.body.scrollTop + document.documentElement.scrollTop; 
  // 计算每次滑动的距离
  let everTop = (number - nowTop) / spacingInex;

  let scrollTimer = setInterval(() => {
    if (spacingInex > 0) {
      spacingInex--;
      ScrollTop(nowTop += everTop);
    } else {
      clearInterval(scrollTimer); // 清除计时器
    }
  }, spacingTime);
};

// 滚动到距离页面顶部500px的位置 动画时间为300ms
// scrolling(500, 300);

// 运用了H5的scrollIntoView方法，这是一个实验中的功能，IE 8以下、Safari 6以下、Safari on iOS 5以下不兼容
const scrollToAnchor = (anchorName) => {
  if (anchorName) {
    // 找到锚点
    let anchorElement = document.getElementById(anchorName);
    // 如果对应id的锚点存在，就跳转到锚点
    if (anchorElement) {
      anchorElement.scrollIntoView({
        behavior: 'auto', // 定义动画过渡效果， "auto"或 "smooth" 之一。默认为 "auto"
        block: 'start', // 定义垂直方向的对齐， "start", "center", "end", 或 "nearest"之一。默认为 "start"
        inline: 'nearest', // 定义水平方向的对齐， "start", "center", "end", 或 "nearest"之一。默认为 "nearest"
      });
    }
  }
}