Adding numbers within object method in javascript

Question

Say I have the following object:

var my_object = {
    value1: "220",
    value2: "100",
    value3_1: "300",
    value3_2: "300",
    value3: function() {
        return +this.value3_1 + +value3_2;
    }
};

What do I need to do to make this work? In console, my_object.value3 returns:

() {
        return +this.value3_1 + +this.value3_2;
    }

..instead of '600'.

Also fix the reference to value3_2 — should be this.value3_2 — Pointy
– Pointy, Commented Oct 28, 2018 at 14:57
Ahh! Of course. It's a function (Method) and thus I need the parenthesis. Thanks. Please feel free to post it as an answer instead of a comment. — Streching my competence
– Streching my competence, Commented Oct 28, 2018 at 14:58
Possible duplicate of Call functions from function inside an object (object literal) — Mohammad
– Mohammad, Commented Oct 28, 2018 at 14:58

niry · Accepted Answer · 2018-10-29 01:37:12Z

2

Use getter

var my_object = {
 value1: 220,
 value2: 100,
 value3_1: 300,
 value3_2: 300,
 get value3() {
    return this.value3_1 + this.value3_2;
 }
};

console.log(my_object.value3);

This way you don't need to "know" which one is a function and which is not.

For example, say you need to read all values, you can do:

Object.keys(my_object).forEach(k => console.log(k, my_object[k]))

Whereas without getter, you'll need to:

Object.keys(my_object).forEach(k => console.log(k, 
    typeof my_object[k] === 'function' ? my_object[k]() : my_object[k]))

edited Oct 29, 2018 at 1:37

answered Oct 28, 2018 at 15:12

niry

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7 Comments

Streching my competence Over a year ago

Perhaps knowing is a good thing? Especially for a newbie like me that is still struggling with syntax. It's there another raccoon for using get? What does is mean? Can't just use it if I don't understand it.

Streching my competence Over a year ago

To me it looks like you are suing that you want to get a prop that doesn't exist (reversed word logic) and it makes me uncomfortable in that I'll remember it.

niry Over a year ago

Updated my answer with examples. newbie or not, you deserve the answers.

Streching my competence Over a year ago

Yeah sorry, that just introduced more questions like "what is key?", "is it a new object, even though my_object is an object literal and not a constructor?", "why write object first?", "Why is forEach appended to key?", "what is 'k'?". Sure, less code, so that's good. Perhaps I can revisit this and utilize it in a few months.

niry Over a year ago

Objects (e.g my_object) are made of key:value pairs. Object.keys() is a function that will return an array of all the keys in a given object. .forEach is an array function that will callback the given function, for each element in the array.

|

ishanbakshi · Accepted Answer · 2018-10-28 15:08:04Z

0

You possibly want to do this :

var my_object = {
 value1: "220",
 value2: "100",
 value3_1: 300,
 value3_2: 300,
 value3: function() {
    return +this.value3_1 + this.value3_2;
 }
};

and then call the function with this : my_object.value3()

Note: I added this in front of value3_2 and I changed the value of value3 _1 and value3_2 to numbers from string be removing the double quotes.

answered Oct 28, 2018 at 15:08

ishanbakshi

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1 Comment

Streching my competence Over a year ago

Perfect! I thought it was weird to have to write the plus in front of the strings, and since I'm using numbers for calculations then this makes more sense of course.

Lakshmi · Accepted Answer · 2018-10-28 19:26:29Z

0

When you are calling a function, you need to use parenthesis (). So it should be my_object.value3().

Also you have to replace value3_2 with this.value3_2

Alternatively, value3_1 and value3_2 are both numbers, so no need to give quotes. Simply you can write 300.

var my_object = {
  value1: 220,
  value2: 100,
  value3_1: 300,
  value3_2: 300,
  value3: function() {
    return this.value3_1 + this.value3_2;
 }
};

answered Oct 28, 2018 at 19:26

Lakshmi

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