如何调用对象的方法？

Question

How would I call my method to my other objects? Been having lots of trouble with everything I've tried. I'm not that confident with this stuff, just looking on how to tell if the object is safe to drive or not.

//Create a constructor function called `Track`. It will accept two parameters - the name of the track and the maximum capacity of the track. 
let track = function(name, capacity){
    this.trackName=name
    this.personnel=0;
    this.cars=[];
    this.cap=capacity;
}


//We'll need a value for the average weight of a person but this value will be the same for all tracks. 
//Add a property `personWeight` on the `Track` prototype so that all instances share the same value. 
track.prototype.personWeight = 200

//Create three methods on the prototype that will calculate track weight, person weight, and if its safe to drive
    function personWeight(){
        personnelWeight = this.personWeight * this.personnel
        return personnelWeight
    }

    function trackWeight(){
        let carsTotal = function myFunc(total, num) {
        return total - num;
    }
        let weightTotal = (this.personnel * this.personWeight) + (this.carsTotal)
        return weightTotal
    }

    function safeToDrive(){
        if(this.trackWeight<this.capacity){
            return true 
        }
    }


//Create two track objects
let trackOne = new track ("Daytona", 25000);
trackOne.cars = [1800, 2400, 2700, 3200, 3600, 3800, 4200]
trackOne.personnel = 10

let trackTwo = new track ("Indiana",15000);
trackTwo.cars = [2000, 2300, 2800, 3000, 3500, 3700, 4000]
trackTwo.personnel = 8


//Call the `safeToDrive` method for truck objects. 

Answer 1

With the code as it is now, you would use safeToDrive.call(trackOne) . However, this is not the straight-forward way you would do it normally.

I guess what you really want is assigning these methods to the prototype:

    track.prototype.safeToDrive = function () {
        if(this.trackWeight<this.capacity){
            return true 
        }
    }

Then you'd call them using trackOne.safeToDrive() .

The same goes for personWeight and trackWeight .

---

A few other observations:

1. Your check for this.capacity won't work because the property is actually called cap and not capacity according to what you set in your constructor.

2. safeToDrive currently returns true or nothing, ie undefined , and not true or false as you would expect.

   You could fix that by either adding an else with return false or simply using return this.trackWeight < this.capacity instead of the whole if condition.

3. Oh, also, your personnelWeight variable is accidentally made global. Add a let before it. To avoid this in the first place, add 'use strict' at the top of your file to get warned about this issue next time.

4. I'm not sure what you are doing with carsTotal there though, I guess that should be a member function as well (otherwise you couldn't even call it using this.carsTotal as you do now). Plus, your indention is wrong there. (Put your file through a beautifier to see what I mean.)

5. Do you mean truck instead of track maybe...?