call() 不适用于 javascript 中的 getter 和 setter

Question

 let Name = { get fullname() { return this.fname + this.last } } function pension() { return this.age > 60 } let firstclass_employee = [{ fname: "sangeth", last: "AV", age: 21, address: { housename: "good house", place: "goodplace", city: "goodtwon", postcode: 121212 }, hobbies: ["driving", "travelling", "sports"] }, { fname: "ramu", last: "kv", age: 29, address: { housename: "etho veedu", place: "vayadi", city: "kalur", postcode: 11111 }, hobbies: ["travelling", "sports"] }] console.log(" objects::\t", Name, "\n", firstclass_employee) //calling a out side function for an object(out side function may be inside an object oe not) console.log("Fullname of first employee::", Name.fullname.call(firstclass_employee[0])) console.log("Pension status of of first emlpoyee::", pension.call(firstclass_employee[0])) console.log("Fullname of 2nd employee::", Name.fullname.call(firstclass_employee[1])) console.log("Pension status of of 2nd emlpoyee::", pension.call(firstclass_employee[1]))

AND getting error---> console.log("Fullname of first employee::", Name.fullname.call(firstclass_employee[0])) ^

TypeError: Name.fullname.call is not a function

Answer 1

remove get - which is not a valid here

let Name = {
   fullname() {
        return this.fname + this.last
    }
}

Answer 2

If you want regular function remove the get and it will work fine. Sorry, I was mistakenly said you have errors in the console.log() part.

 let Name = { fullname() { return this.fname + this.last } } function pension() { return this.age > 60 } let firstclass_employee = [{ fname: "sangeth", last: "AV", age: 21, address: { housename: "good house", place: "goodplace", city: "goodtwon", postcode: 121212 }, hobbies: ["driving", "travelling", "sports"] }, { fname: "ramu", last: "kv", age: 29, address: { housename: "etho veedu", place: "vayadi", city: "kalur", postcode: 11111 }, hobbies: ["travelling", "sports"] }] console.log(" objects::\t", Name, "\n", firstclass_employee) //calling a out side function for an object(out side function may be inside an object oe not) console.log("Fullname of first employee::", Name.fullname.call(firstclass_employee[0])) console.log("Pension status of of first emlpoyee::", pension.call(firstclass_employee[0])) console.log("Fullname of 2nd employee::", Name.fullname.call(firstclass_employee[1])) console.log("Pension status of of 2nd emlpoyee::", pension.call(firstclass_employee[1]))

Answer 3

As far as why the call() is invalid is that Name.fullname is not exposed as a function. It is exposed the same way as a field would be, eg

const Name = {
  fullname: 'Bob'
};

With that structure, you wouldn't expect to be able to call Name.fullname.call , right? But for the purposes of getting the value, that's what the prior code exposed to the outside world (the difference with the field being that you can set the value, whereas with a getter and no setter, the property is read only).

The get essentially tells the JavaScript engine that, whenever someone asks for the value of fullname , give them the value of the fname and last properties concatenated together.

Thus, when you ask for Name.fullname.call(firstclass_employee[0]) it first finds Name . Then it asks for the value of fullname . It gets back NaN , because this is the Name object and it doesn't have fname or last properties, and it tries to coerce the first undefined (from this.fname ) to a Number for the addition operator, and gets NaN . Then it tries to get the call function on NaN , and there is no such thing, so it throws an error.

---

It appears as though you want to be able to get a full name from any object that has fname and last properties. I would suggest using static method for that rather than an instance property getter.

Similarly, a static method would work for determining employees who get a pension.

Personally, I would just create a class or series of class es that I could compose together to bring this functionality together, rather than trying to use call , but that's me.

 const Name = { fullName(obj) { return `${obj.fname} ${obj.last}`; } }; const Pay = { getsPension(obj) { return obj.age > 60; } } let firstclass_employee = [{ fname: "sangeth", last: "AV", age: 21, address: { housename: "good house", place: "goodplace", city: "goodtwon", postcode: 121212 }, hobbies: ["driving", "travelling", "sports"] }, { fname: "ramu", last: "kv", age: 29, address: { housename: "etho veedu", place: "vayadi", city: "kalur", postcode: 11111 }, hobbies: ["travelling", "sports"] }] console.log('should be sangeth AV: ', Name.fullName(firstclass_employee[0])); console.log('should be false: ', Pay.getsPension(firstclass_employee[0]));