转自https://www.cnblogs.com/itjeff/p/11168310.html

str为要去除空格的字符串:
去除所有空格:   
str   =   str.replace(/\s+/g,"");       
去除两头空格:   
str   =   str.replace(/^\s+|\s+$/g,"");
去除左空格：
str=str.replace( /^\s*/, '');
去除右空格：
str=str.replace(/(\s*$)/g, "");

SCRIPT LANGUAGE="JavaScript">    
<!--    
//出处:网上搜集    
// Trim() , Ltrim() , RTrim()    
String.prototype.Trim = function()    
{    
returnthis.replace(/(^\s*)|(\s*$)/g, "");    
}    
String.prototype.LTrim = function()    
{    
returnthis.replace(/(^\s*)/g, "");    
}    
String.prototype.RTrim = function()    
{    
returnthis.replace(/(\s*$)/g, "");    
}    
//-->    
</SCRIPT>    
<input type="text" value="    前后都是空格     " id="space">    
<input type="button" value="去前后空格" onclick="javascript:document.getElementById('space').value=document.getElementById('space').value.Trim();document.getElementById('space').select();">    
<input type="button" value="去前空格" onclick="javascript:document.getElementById('space').value=document.getElementById('space').value.LTrim();document.getElementById('space').select();">    
<input type="button" value="去后空格" onclick="javascript:document.getElementById('space').value=document.getElementById('space').value.RTrim();document.getElementById('space').select();">    
<input type="button" value="还原" onclick="javascript:document.getElementById('space').value='      前后都是空格     ';">    
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去除所有空格: 
str = str.replace(/\s+/g,"");
去除两头空格: 
str = str.replace(/^\s+|\s+$/g,"");
去除空格(TimeSheet用过)
arg0=arg0.replace(/\s+$|^\s+/g,"");