【转】项目中遇到的bug（web前端-持续更新）

蔚落 2022-05-26 04:55 208阅读 0赞

## 写代码容易遇到各种奇怪的BUG，推荐使用[Fundebug][]做线上bug实时监控。 ##

## input放在a标签里面单击不能获取input的光标（IE环境下） ##

双击才可以获得焦点，目前有的解决方案：

*  不要给a标签添加href属性；
 *  不要在外面套上a标签。

## 隐藏input标签的光标 ##

项目需求：input值json加载，只读+光标隐藏，通用的解决方案有其他标签模拟，但是不能改input   
所以解决方案为给input加下面这两个属性：

//只读 
    readonly="readonly" 
    //隐藏光标
    unselectable="on"

## 返回私有数组 ##

返回数组的一个副本，这样改动就不会影响原数组，只是副本而已

var array = (function () { 
           var days = ['Mo', 'Tu', 'We', 'Th', 'Fr', 'Sa', 'Su'];
            return {
                getDays: function () { 
                    return days.slice();
                }
            }
        })()

## jquery选择器的扩展 ##

//jQuery contains 选择器，对Contains查找的内容不区分大小写
    jQuery.expr[':'].Contains = function (a, i, m) { 
        return jQuery(a).text().toUpperCase()
            .indexOf(m[3].toUpperCase()) >= 0;
    };

例子

$('div:Contains("john")') //会选择到两个div

## 当一个变量被声明后，扩充其属性并不会改变原数据类型 ##

var a = 'foo'; 
    a[1] = 'O'; 
    console.log(0.1+0.2==0.3||a); //'foo'

## 闭包是函数的嵌套定义，而不是函数的嵌套调用 ##

function foo(){ 
        console.log(a);
    }
    function bar () { 
        var a = 3; 
        foo(); 
    }
    var a = 2;
    bar(); //2

## DOMContentLoaded兼容IE9以下版本 ##

//jQuery的实现
    
          // Mozilla, Opera and webkit nightlies currently support this event
          if ( document.addEventListener ) {
              // Use the handy event callback
              document.addEventListener( "DOMContentLoaded", DOMContentLoaded, false );
    
              // A fallback to window.onload, that will always work
              window.addEventListener( "load", jQuery.ready, false );
    
              // If IE event model is used
          } else if ( document.attachEvent ) {
              // ensure firing before onload,
              // maybe late but safe also for iframes
              document.attachEvent( "onreadystatechange", DOMContentLoaded );
    
              // A fallback to window.onload, that will always work
              window.attachEvent( "onload", jQuery.ready );
    
              // If IE and not a frame
              // continually check to see if the document is ready
              var toplevel = false;
    
              try {
                  toplevel = window.frameElement == null;
              } catch(e) {}
    
              if ( document.documentElement.doScroll && toplevel ) {
                  doScrollCheck();
              }
          }
    
            //函数DOMContentLoaded的赋值
            if ( document.addEventListener ) {
                DOMContentLoaded = function() {
                    document.removeEventListener( "DOMContentLoaded", DOMContentLoaded, false );
                    jQuery.ready();
                };
    
            } else if ( document.attachEvent ) {
                DOMContentLoaded = function() {
                    // Make sure body exists, at least, in case IE gets a little overzealous (ticket #5443).
                    if ( document.readyState === "complete" ) {
                        document.detachEvent( "onreadystatechange", DOMContentLoaded );
                        jQuery.ready();
                    }
                };
            }
    
    // The DOM ready check for Internet Explorer
            function doScrollCheck() {
                if ( jQuery.isReady ) {
                    return;
                }
    
                try {
                    // If IE is used, use the trick by Diego Perini
                    // http://javascript.nwbox.com/IEContentLoaded/
                    document.documentElement.doScroll("left");
                } catch(e) {
                    setTimeout( doScrollCheck, 1 );
                    return;
                }
    
                // and execute any waiting functions
                jQuery.ready();
            }
    
    //网友的实现
        // @win window reference
        // @fn function reference
        function contentLoaded(win, fn) {
    
            var done = false, top = true,
    
                    doc = win.document,
                    root = doc.documentElement,
                    modern = doc.addEventListener,
    
                    add = modern ? 'addEventListener' : 'attachEvent',
                    rem = modern ? 'removeEventListener' : 'detachEvent',
                    pre = modern ? '' : 'on',
    
                    init = function(e) {
                        if (e.type == 'readystatechange' && doc.readyState != 'complete') {
                            return;
                        }
    
                        //load事件在win上，移除事件监听(readystatechange, DOMContentLoaded, load)
                        (e.type == 'load' ? win : doc)[rem](pre + e.type, init, false);
    
                        //保证fn只执行一次
                        if (!done && (done = true)) fn.call(win, e || e.type);
                    },
    
                    poll = function() {
                        try { root.doScroll('left'); } catch(e) { setTimeout(poll, 50); return; }
                        init('poll');
                    };
    
            if (doc.readyState == 'complete') fn.call(win, 'lazy');
            else {
                if (!modern && root.doScroll) {
                    try { top = !win.frameElement; } catch(e) { }
                    if (top) poll();
                }
                doc[add](pre + 'DOMContentLoaded', init, false); //触发时，doc.readyState为'interactive'
                doc[add](pre + 'readystatechange', init, false); //会触发两次，readystatechange先触发，再触发DOMContentLoaded, 最后才是load
                win[add](pre + 'load', init, false);
            }
    
        }

## document.querySelectorAll和getElementsByTagName的区别 ##

//html代码
    <ul>
        <li>a</li>
        <li>b</li>
        <li>c</li>
    </ul>
    
    //script代码
        var ul = document.querySelector('ul');
        var li = ul.querySelectorAll('li'),
                tagLi = ul.getElementsByTagName('li'); //动态取值 
        ul.appendChild(document.createElement('li'));
        console.log(li.length); //3 li.toString()为[object NodeList]    console.log(tagLi.length); //4 tagLi.toString()为[object HTMLCollection]

### 参考： ###

1.  [Fundebug：小程序错误监控支持用户行为回溯][Fundebug 1]
2.  [怪异的JavaScript系列(一)][JavaScript]
3.  [怪异的JavaScript系列(二)][JavaScript 1]

[Fundebug]: https://www.fundebug.com
[Fundebug 1]: https://blog.fundebug.com/2018/04/10/fundebug-wxjs-0.1.2/
[JavaScript]: http://https//blog.fundebug.com/2018/04/03/javascript-werid-series-1/
[JavaScript 1]: http://https//blog.fundebug.com/2018/04/12/javascript-werid-series-2/