如果不使用类库或者没有自己的类库，储备一些常用函数总是有好处的。

1.$()

function $() {
    var elements = [];
    for (var i = 0; i < arguments.length; i++) {
        var element = arguments[i];
        if (typeof element == 'string')
            element = document.getElementById(element);
        if (arguments.length == 1)
            return element;
        elements.push(element);
    }
    return elements;
}

2.getStyle()与setStyle()

function setStyle(el,prop,value){
   if(prop == "opacity" && !+"\v1"){
     //IE7 bug:filter 滤镜要求 hasLayout=true 方可执行（否则没有效果）
     if (!el.currentStyle || !el.currentStyle.hasLayout) el.style.zoom = 1;
     prop = "filter";
     if(!!window.XDomainRequest){
       value ="progid:DXImageTransform.Microsoft.Alpha(style=0,opacity="+value*100+")";
     }else{
       value ="alpha(opacity="+value*100+")"
     }
   }
   el.style.cssText += ';' + (prop+":"+value);
 }
 
 function getStyle(el, style){
   if(!+"\v1"){
     style = style.replace(/\-(\w)/g, function(all, letter){
       return letter.toUpperCase();
     });
     return el.currentStyle[style];
   }else{
     return document.defaultView.getComputedStyle(el, null).getPropertyValue(style)
   }
 }

3.getCookie(), setCookie(), deleteCookie()

function getCookie( name ) {
    var start = document.cookie.indexOf( name + "=" );
    var len = start + name.length + 1;
    if ( ( !start ) && ( name != document.cookie.substring( 0, name.length ) ) ) {
        return null;
    }
    if ( start == -1 ) return null;
    var end = document.cookie.indexOf( ';', len );
    if ( end == -1 ) end = document.cookie.length;
    return unescape( document.cookie.substring( len, end ) );
}
function setCookie( name, value, expires, path, domain, secure ) {
    var today = new Date();
    today.setTime( today.getTime() );
    if ( expires ) {
        expires = expires * 1000 * 60 * 60 * 24;
    }
    var expires_date = new Date( today.getTime() + (expires) );
    document.cookie = name+'='+escape( value ) +
        ( ( expires ) ? ';expires='+expires_date.toGMTString() : '' ) + //expires.toGMTString()
        ( ( path ) ? ';path=' + path : '' ) +
        ( ( domain ) ? ';domain=' + domain : '' ) +
        ( ( secure ) ? ';secure' : '' );
}
function deleteCookie( name, path, domain ) {
    if ( getCookie( name ) ) document.cookie = name + '=' +
            ( ( path ) ? ';path=' + path : '') +
            ( ( domain ) ? ';domain=' + domain : '' ) +
            ';expires=Thu, 01-Jan-1970 00:00:01 GMT';
}

4.inArray()

var inArray = function (arr,value) {
    for (var i=0,l = arr.length ; i <l ; i++) {
        if (arr[i] === value) {
            return true;
        }
    }
    return false;
};

5.insertAfter()

function insertAfter(parent, node, referenceNode) {
    parent.insertBefore(node, referenceNode.nextSibling);
}

6.toggle()

function toggle(obj) {
    var el = document.getElementById(obj);
    if ( el.style.display != 'none' ) {
        el.style.display = 'none';
    }
    else {
        el.style.display = '';
    }
}

7.getElementsByClass()

var getElementsByClassName = function (searchClass, node,tag) {
    if(document.getElementsByClassName){
        return  document.getElementsByClassName(searchClass)
    }else{
        node = node || document;
        tag = tag || "*";
        var classes = searchClass.split(" "),
        elements = (tag === "*" && node.all)? node.all : node.getElementsByTagName(tag),
        patterns = [],
        returnElements = [],
        current,
        match;
        var i = classes.length;
        while(--i >= 0){
            patterns.push(new RegExp("(^|\\s)" + classes[i] + "(\\s|$)"));
        }
        var j = elements.length;
        while(--j >= 0){
            current = elements[j];
            match = false;
            for(var k=0, kl=patterns.length; k<kl; k++){
                match = patterns[k].test(current.className);
                if (!match)  break;
            }
            if (match)  returnElements.push(current);
        }
        return returnElements;
    }
}

8.addLoadEvent()

var addLoadEvent = function(fn) {
  var oldonload = window.onload;
  if (typeof window.onload != 'function') {
    window.onload = fn;
  }else {
    window.onload = function() {
      oldonload();
      fn();
    }
  }
}

9.addEvent()

function addEvent(elm, evType, fn, useCapture) {
  if (elm.addEventListener) {
    elm.addEventListener(evType, fn, useCapture);//DOM2.0
    return true;
  }
  else if (elm.attachEvent) {
    var r = elm.attachEvent('on' + evType, fn);//IE5+
    return r;
  }
  else {
    elm['on' + evType] = fn;//DOM 0
  }
}