更改 Javascript 中的构造函数 class 中属性的默认值

Question

I have a class Action below. Default values for _actionOver and _peopleAffected are defined.

class Action {
    constructor(staffName, description, actionOver, peopleAffected){
        this._staffName=staffName;
        this._description=description;
        this._actionOver=false;
        this._peopleAffected=0;
    }

Now I define a new object of this class and change values for actionOver and _peopleAffected

let a= new Action ('Raul', 'Goal 1: Qaulity Education', true,10);

When I print this in console

console.log(a._actionOver);   *// gives false
console.log(a._peopleAffected);  *// gives 0*

Should not it give true and 10 as output, if i have changed values in object. If not how do I change default value of an constructor attribute?

Answer 1

You're just ignoring the constructor arguments and always assign the same initial value.
I guess you actually wanted to use default parameter values ?

class Action {
    constructor(staffName, description, actionOver = false, peopleAffected = 0){
//                                                ^^^^^^^^                ^^^^
        this._staffName = staffName;
        this._description = description;
        this._actionOver = actionOver;
//                         ^^^^^^^^^^
        this._peopleAffected = peopleAffected;
//                             ^^^^^^^^^^^^^^
    }

Answer 2

You're not assigning a default value, you're just assigning a value and ignoring the values passed as arguments.

Once you defined your default:

    this._actionOver=false;

You must check if other values have been passed via arguments and overwrite the defaults:

    this._actionOver=false;
    if (actionOver) this._actionOver = actionOver;

You can do a one liner:

   this._actionOver = actionOver || false;

Or just use function parameter defaults:

    constructor(staffName, description, actionOver = false, peopleAffected = 0){
        // ....
        this._actionOver=actionOver;
    }