var array = {
    expand : function(source,size){
        var target = new Array(size);
        var span = (size / source.length);
        for(var i = 0 ; i < source.length ;i++ ){
            var range = [ Math.floor(i * span) , Math.floor(( i + 1 ) * span)];
            target.fill(source[i],...range);
        }
        return target;
    },
    extract : function(source,size){
        var target = new Array(size);
        var span = (source.length / size);
        for(var i = 0 ; i < size ;i++ ){
            var range = [ Math.floor(i * span) , Math.floor(( i + 1 ) * span)];
            target[i] = Math.max.apply(null,source.slice(...range));
        }
        return target;
    }
  }
//   数组原型对象重新赋值一个函数,   新定义的expand与extract是要赋值的函数
  Array.prototype.expand = function (size) { return array.expand(this,size);}
  Array.prototype.extract = function (size) { return array.extract(this,size);  }

  Uint8Array.prototype.__proto__.expand = function (size) { return array.expand(this,size);}
  Uint8Array.prototype.__proto__.extract = function (size) { return array.extract(this,size);  }