Set JavaScript Object value with a function

Question

Im trying to set an Object value with a function. essentially, im trying to calculate the total values in an object up to a certain point, which is the limit variable im passing to the calculateTotal function.

seems like im doing it wrong, any suggestions?

var sc = 0.75
com = 2197.63,
  user_input = 400,
  f11_total = 0;

var v = {
  "a": com,
  "b": (com * 0.06 * sc),
  "c": (com * 0.09 * sc),
  "d": (215.54 * Math.pow(sc, 2)),
  "e": (299.36 * sc),
  "f": 328.76,
  "g": ((com * 0.048) * (user_input / 400)),
  "h": (com * 0.01),
  "3.6": 0.036,
  "total": function() {
    calculateTotal(3.6);
  }
};

function calculateTotal(limit) {
  for (var k in v) {
    if (k == limit) return (f11_total * v[k]);
    f11_total += v[k];
  }
}

console.log(calculateTotal(3.6));

thanks!

This sounds like a pretty good chance to use get. I realize this question is "complete" but decided to throw an alternative in the ring anyway. — Tyler Roper
– Tyler Roper, Commented Aug 23, 2017 at 21:11

Jonathan.Brink · Accepted Answer · 2017-08-23 20:29:23Z

3

The value of the total member is getting set to the function you have defined, not it's return value.

As @Santi points out, we can't reference v inside calculateTotal until v has finished being declared.

An approach here could be to populate total after v has been declared like this:

var v = {
  "a": com,
  "b": (com * 0.06 * sc),
  "c": (com * 0.09 * sc),
  "d": (215.54 * Math.pow(sc, 2)),
  "e": (299.36 * sc),
  "f": 328.76,
  "g": ((com * 0.048) * (user_input / 400)),
  "h": (com * 0.01),
  "3.6": 0.036  
};
v.total = calculateTotal(3.6);

edited Aug 23, 2017 at 20:29

answered Aug 23, 2017 at 19:59

Jonathan.Brink

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5 Comments

Lookin Punk Over a year ago

i tried that but for some reason im getting an undefined result, what am i missing?

Tyler Roper Over a year ago

@Jonathan.Brink I believe OP wants this to return 116.88649793999998, however the example above will return 0. And k == limit will always evaluate to true. It's the property before "total".

Jonathan.Brink Over a year ago

@Santi thanks, I missed the return statement in there. I updated my answer

Tyler Roper Over a year ago

@Jonathan.Brink I believe that v is undefined because you're referencing v inside it's own initialization.

Lookin Punk Over a year ago

once k == limit is true (and i check, it returns true just once), the function is suppose to return 116.886... if i call the function from outside the object, it works fine.

Tyler Roper · Accepted Answer · 2017-08-23 21:17:32Z

The primary issue is that you're returning a function instead of an actual value.

Jonathan's answer is concise and correct, however I figured I'd supply you with a modern alternative using get.

It requires no manipulation/initialization of the object, is entirely self-contained, and will recalculate if/when the object is modified.

var sc = 0.75
com = 2197.63,
  user_input = 400;

var v = {
  "a": com,
  "b": (com * 0.06 * sc),
  "c": (com * 0.09 * sc),
  "d": (215.54 * Math.pow(sc, 2)),
  "e": (299.36 * sc),
  "f": 328.76,
  "g": ((com * 0.048) * (user_input / 400)),
  "h": (com * 0.01),
  "3.6": 0.036,
  get total() {
    var f11_total = 0;
    for (var k in this) {
      if (k == 3.6) return (f11_total * this[k]);
      f11_total += this[k];
    }
  }
}

console.log("v.total = " + v.total);
v.f = 100;
console.log("f changed to 100");
console.log("v.total = " + v.total);

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