属性的读写
//属性添加
var obj = {x:1,y:2};
obj.z = 3;
obj["m"] = 4;
//属性的读取
var obj = {x: 1, y: 2, z: 3, m: 4};
for(p in obj){
console.info(p);
}
属性的删除
var person = {age:45,name:"tom"};
person.age //
delete person.age //true
person.age //undefined
属性标签【configurable】
var obj = {age:1,name:"cat"};
Object.getOwnPropertyDescriptor(obj,'age');
//Object {value: 1, writable: true, enumerable: true, configurable: true};
//getOwnPropertyDescriptor()方法--查看age的属性标签
Object.defineProperty(obj,'age',{configurable:false});
//设置age属性configurable标签为false【表示age属性不可配置】
Object.getOwnPropertyDescriptor(obj,'age');
Object {value: 1, writable: true, enumerable: true, configurable: false};
delete obj.age //false
obj.age //
不能删除的特殊情况
1 var定义的全局变量与局部变量
var globalValue = 90;
delete globalValue //false
(function(){
var localValue = 90;
return delete localValue;
})(); //false
//隐式的创建全局变量是可以删除的
yinshi = 90;
delete yinshi //true
2 全局定义函数与局部定义的函数
function test(){}
delete test; //false
(function(){
function localfunction(){};
return delete localfunction; //false
})();
判断属性是否存在
var dog = {};
dog.name = "dong";
dog.age = 89;
"name" in dog; //true
"abc" in dog //false
"toString" in dog //true //in操作符 会查找原型链。
dog.hasOwnProperty('name'); //true
dog.hasOwnProperty('toString'); //false 不查找原型链用hasOwnProperty方法
属性的枚举
var o = {x:1,y:2,z:3}
for(key in o){
console.info(key) //x y z
}
Object.keys(o) //["x", "y", "z"]
【Enumerable】属性标签
var o = {x:1,y:2,z:3}
//propertyIsEnumerable 检测属性的【Enumerable】为true or false
o.propertyIsEnumerable('x') //true
o.propertyIsEnumerable('y') //true
o.propertyIsEnumerable('z') //true
o.propertyIsEnumerable('toString') //false
//只有propertyIsEnumerable为true的属性，可以枚举
for(key in o){
console.info(key) //x y z
}
var o = {x:1,y:2,z:3}
//设置对象的x属性【enumerable】标签为false
Object.defineProperty(o,'x',{enumerable:false})
o.propertyIsEnumerable('x') //false
for(key in o){
console.info(key) //y z
}