javascript笔记

存取器属性：

var o={$n:0,

get n(){return this.$n;},

set n(n){this.$n=n;}

};

o.n=5;

o.n //5;

o.hasOwnProperty("$n"); //true;

o.propertyIsEnumerable("toString"); //false;

Object.getOwnPropertyDescriptor(o,"$n");

Object.defineProperty(o,"$n",{value:7,writable:false,enumerable:true})

Object.prototype.toString.call(p);//判断类型
p instanceof Point;
p.constructor===Point;
typeof p;//will return Object.

Object.preventExtention(o);

Object.isExtensible(o);

function fun(){

arguments.length;实参个数

this.length;//形参个数

}

function Point(x,y){this.x=x;this.y=y;}

Point.prototype.show=function(){console.log(x+y);}

var p=new Point(3,4);

p.constructor===Point //true;

----------------------------------

function Point(x, y) {
  this.x = x;
  this.y = y;
}
Point.prototype = {
  constructor:Point,
  show: function () {
    console.log(x + y);
  }
}
var p = new Point(3, 4);
p.constructor === Point //true;

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javascript: function enumeration(nameToValues) {
  var enumeration = function () {
    throw 'can\'t instantiate the instance!'
  };
  var enumerator = function () {
  };
  var proto = enumerator.prototype = {
    constructor: enumeration,
    toString: function () {
      return this.name;
    },
    valueOf: function () {
      return this.value;
    },
    toJson: function () {
      return this.name;
    }
  };
  enumeration.values = [
  ];
  for (var name in nameToValues) {
    var e = new enumerator;
    e.name = name;
    e.value = nameToValues[name];
    enumeration[name] = e;
    enumeration.values.push(e);
  }
  return enumeration;
}
var Cards = enumeration({
  Red: 1,
  Green: 2,
  Blue: 3
});
Cards['Red']