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小技巧

码检测浏览器是否支持 position:fixed​

var div = document.createElement('div');
div.style.cssText = 'display:none;position:fixed;z-index:100;';
body.appendChild(div);
console.log(window.getComputedStyle(div).position != 'fixed');
function isSupportFixed() {
  var userAgent = window.navigator.userAgent,
      ios = userAgent.match(/(iPad|iPhone|iPod)\s+OS\s([\d_\.]+)/),
      ios5below = ios && ios[2] && (parseInt(ios[2].replace(/_/g, '.'), 10) < 5),
      operaMini = /Opera Mini/i.test(userAgent),
      body = document.body,
      div, isFixed;
  div = document.createElement('div');
  div.style.cssText = 'display:none;position:fixed;z-index:100;';
  body.appendChild(div);
  isFixed = window.getComputedStyle(div).position != 'fixed';
  body.removeChild(div);
  div = null;
  return !!(isFixed || ios5below || operaMini);
}

高亮所有元素​

[].forEach.call($$("*"), function(a) {
  a.style.outline =
    "1px solid #" + (~~(Math.random() * (1 << 24))).toString(16);
});

计算中文长度​

function getRealLen( str ) {
    return str.replace(/[^\x00-\xff]/g, '__').length; //这个把所有双字节的都给匹配进去了
}

中文截断​

function beautySub( str, len) {
    var reg = /[\u4e00-\u9fa5]/g,    //专业匹配中文
  slice = str.substring(0,len),
  realen = len - ( ~~( slice.match(reg) && slice.match(reg).length ) );
  return slice.substring(0, realen ? realen : 1);
}

全局错误上报

window.onerror = `function (errorMsg, fileLoc, linenumber) {
    var s = 'url: ' + document.URL + '\nfile:  ' + fileLoc
        + '\nline number: ' + linenumber
        + '\nmessage: ' + errorMsg;
    Log.error(s);       // 发给服务器统计监控
    console.log(s);
}`

参考​