js属性对象的hasOwnProperty方法

Posted 2021-03-12 巷陌i

判断自生属性与继承性

 

 function foo() {
            this.name = ‘foo‘
            this.sayHi = function () {
                console.log(‘Say Hi‘)
            }
        }

        foo.prototype.sayGoodBy = function () {
            console.log(‘Say Good By‘)
        }

        var myPro = new foo()

        console.log(myPro.name) // foo
        console.log(myPro.hasOwnProperty(‘name‘)) // true
        console.log(myPro.hasOwnProperty(‘toString‘)) // false
        console.log(myPro.hasOwnProperty(‘hasOwnProperty‘)) // fasle
        console.log(myPro.hasOwnProperty(‘sayHi‘)) // true
        console.log(myPro.hasOwnProperty(‘sayGoodBy‘)) // false
        console.log(‘sayGoodBy‘ in myPro) // true

判断自生属性是否存在

var o = new Object();
o.prop = ‘exists‘;
function changeO() {
    o.newprop = o.prop;
    delete o.prop;
}
console.log(o.hasOwnProperty(‘prop‘));  // true
changeO();
console.log(o.hasOwnProperty(‘prop‘));  // false

遍历一个对象的所有自身属性

在看开源项目的过程中，经常会看到类似如下的源码。for...in循环对象的所有枚举属性，然后再使用hasOwnProperty()方法来忽略继承属性。

var buz = {
    fog: ‘stack‘
};

for (var name in buz) {
    if (buz.hasOwnProperty(name)) {
        alert("this is fog (" + name + ") for sure. Value: " + buz[name]);
    }
    else {
        alert(name); // toString or something else
    }
}