JS中实现Trim()，TrimStart()，TrimEnd() 的方法

//去除字符串头尾空格或指定字符  
    String.prototype.Trim = function (c) {
        if (c == null || c == "") {
            var str = this.replace(/^s*/, '');
            var rg = /s/;
            var i = str.length;
            while (rg.test(str.charAt(--i)));
            return str.slice(0, i + 1);
        }
        else {
            var rg = new RegExp("^" + c + "*");
            var str = this.replace(rg, '');
            rg = new RegExp(c);
            var i = str.length;
            while (rg.test(str.charAt(--i)));
            return str.slice(0, i + 1);
        }
    }
    //去除字符串头部空格或指定字符  
    String.prototype.TrimStart = function (c) {
        if (c == null || c == "") {
            var str = this.replace(/^s*/, '');
            return str;
        }
        else {
            var rg = new RegExp("^" + c + "*");
            var str = this.replace(rg, '');
            return str;
        }
    }
    
    //去除字符串尾部空格或指定字符  
    String.prototype.trimEnd = function (c) {
        if (c == null || c == "") {
            var str = this;
            var rg = /s/;
            var i = str.length;
            while (rg.test(str.charAt(--i)));
            return str.slice(0, i + 1);
        }
        else {
            var str = this;
            var rg = new RegExp(c);
            var i = str.length;
            while (rg.test(str.charAt(--i)));
            return str.slice(0, i + 1);
        }
    }
    
    调用方法：
    var str=,a,b,c,d,;
    str=str.TrimStart(",");
    //str的值为 a,b,c,d,