Example of what i'm trying to achieve

I want to make an object in react which will calculate one its key value from other keys using this function and the 'this' keyword so that I can use this function dynamically with many input fields object.

func = function (c) {
    return this.a   this.b   c;
};

obj1 = {
    a: 1,
    b: 2,
    value: func(5),
};

obj2 = [
    { a: 2, b: 3, value: func(6) },
    {
        a: 4,
        b: 5,
        value: func(7),
    },
];

// expected result
console.log(obj1.value); // 8
console.log(obj2[0].value); // 16

CodePudding user response：

I guess the simplest solution would to flip this around: Pass the object to the function, let it add the property and return the very same object:

const func = function (obj, c) {
  obj.value = obj.a   obj.b   c;
  return obj;
};

const obj1 = func({
    a: 1,
    b: 2,
}, 5);

const obj2 = [
    func({ a: 2, b: 3 }, 6),
    func({
        a: 4,
        b: 5,
    }, 7),
];

// expected result
console.log(obj1.value); // 8
console.log(obj2[0].value); // 16

(no idea how the second example would result in 16 though)

CodePudding user response：

At the moment func is called, this is set to window object, because the object you want to use it in, doesn't exist yet.

You can try returning a function from func

const func = function(c) {
  return function() {
    return this.a   this.b   c
  }
}

const obj1 = {
  a: 1,
  b: 2,
  value: func(5),
}

const obj2 = [{
    a: 2,
    b: 3,
    value: func(6)
  },
  {
    a: 4,
    b: 5,
    value: func(7)
  }
]

// expected result
console.log(obj1.value()) // 8
console.log(obj2[0].value()) // 11