js 单例模式的实现方式----闭包和构造函数内部判断

var singleton = function( fn ){
   var result;
    return function(){
       return result || ( result = fn .apply( this, arguments ) );
    }
}
//test
function aa(){}
var a = aa()
var b = aa()
a===b

function Construct(){
    // 确保只有单例
    if( Construct.unique !== undefined ){

        return Construct.unique; 

    }
    // 其他代码

    this.name = "Construct";
    Construct.unique = this;

}
//test
var t1 = new Construct() ;
var t2 = new Construct() ;
t1 === t2