有两种方法：

1. 改string 的prototype

    String.prototype.trim = function() {  
        return this.replace(/^\s+|\s+$/g,"");  
    }  
    String.prototype.ltrim = function() {  
        return this.replace(/^\s+/,"");  
    }  
    String.prototype.rtrim = function() {  
        return this.replace(/\s+$/,"");  
    }  

2. 如果不想改string的prototype，可以单独写function

    function trim(stringToTrim) {  
        return stringToTrim.replace(/^\s+|\s+$/g,"");  
    }  
    function ltrim(stringToTrim) {  
        return stringToTrim.replace(/^\s+/,"");  
    }  
    function rtrim(stringToTrim) {  
        return stringToTrim.replace(/\s+$/,"");  
    }