using value from previous object property function

Question

Cannot use value from previous object property function starting(); when trying to combine in output below; getting NaN for timeTaken(); function. Presumably starting isn't reporting within that function, any suggestions?

  starting : function() {
     return this.slow * this.driveTime + " mph ";
  },
  timeTaken : function() { 
     return this.starting / this.driveTime + " seconds ";
  },

document.getElementById("car").innerHTML = car.starting() +  car.timeTaken();

Should I rather try to nest both functions in same one function? I'm open to more optimal methods.

Full object code:

var car = {
  cruise: "35",
  slow: "5",
  stop: "0",
  driveTime: "4",
  starting : function() {
     return this.slow * this.driveTime + " mph ";
  },
  timeTaken : function() { 
       return this.starting / this.driveTime + " seconds ";
  },
 };

2 guesses: 1. Shouldn't you make a function call in return: "return this.starting() / ...." . and the second guess, you append the 'mph' which makes the return value of the starting() to string, and try to divide the string to another string. — Gagik Sukiasyan
– Gagik Sukiasyan, Commented Mar 12, 2017 at 20:02
I thought about that, and omitted extra text and still get NaN error. — Lieutenant Dan
– Lieutenant Dan, Commented Mar 12, 2017 at 20:04

Community · Accepted Answer · 2017-05-23 10:30:02Z

6

That's because this.starting is a function. Basically what you are asking JavaScript to do is "take the starting function and divide it by this.driveTime". This is undefined.

What I'm guessing you want is something like this:

var car = {
  cruise: 35,
  slow: 5,
  stop: 0,
  driveTime: 4,
  starting: function() {
    return this.slow * this.driveTime;
  },
  timeTaken: function() {
    return this.starting() / this.driveTime;
  },
  toString: function() {
    return this.starting() + " mph " + this.timeTaken() + " seconds ";
  }
};

console.log(car.toString());
console.log(car.starting());
console.log(car.timeTaken());

Note that I changed starting() and timeTaken() to just return numbers (rather than "x mph" or "x seconds"). This allows you to do math on the results from those functions.

I added the toString() function to make it easier to get a string representation of the data that I'm assuming you wanted to print out.

EDIT: As noted by Peter Behr's answer, you should store cruise, slow stop, and driveTime as numbers rather than strings. I have updated my example to show this.

Further Reading

JavaScript data types and data structures at MDN

edited May 23, 2017 at 10:30

CommunityBot

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answered Mar 12, 2017 at 20:03

Sumner Evans

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2 Comments

Lieutenant Dan Over a year ago

Thanks! so, I have to do the math within another separate function basically?

Sumner Evans Over a year ago

@Cage, you could think of it like that. The most important thing to look at is what each function is returning. If you return something that is a number, as I am for starting and timeTaken, you can do math on its result. Whereas if you return a string, like the toString function, you can only do string operations with it.

Peter Behr · Accepted Answer · 2017-03-12 20:11:09Z

2

Additionally, you're doing math on strings, which isn't a great idea. Make the object properties numbers to begin with.

edited Mar 12, 2017 at 20:11

answered Mar 12, 2017 at 20:03

Peter Behr

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Comments

user5741800 · Accepted Answer · 2017-03-12 20:02:20Z

0

starting method return a String so divide a string by a number will result as NaN

answered Mar 12, 2017 at 20:02

user5741800

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