Javascript Function Global Variable undefined?

Question

I want to create some gauges, but my Gauge object remains undefined.

var doesntwork;
function create_gauge(name, id,  min,  max,  title,  label) {
  name = new JustGage({
    id: id,
    value: 0,
    min: min,
    max: max,
    donut: false,
    gaugeWidthScale: 0.3,
    counter: true,
    hideInnerShadow: true,
    title: title,
    label: label,
    decimals: 2
  });
}
create_gauge(doesntwork, "g2", 0, 100, "Füllstand", "%");
console.log(doesntwork); //undefined

why? can't i pass variables to a function?

Primitives are passed by value, and doesntwork is undefined - a primitive. So if you modify it in the function as name, it has no effect on the doesntwork variable. Why don't you just return the result from new JustGage from the function? — Karl Reid
– Karl Reid, Commented Sep 26, 2017 at 16:16
its a javascript add-on to create gauges. see github.com/toorshia/justgage — David
– David, Commented Sep 26, 2017 at 16:16
Indeed, one cannot pass references to variables to functions, you can only pass values. You could try passing a string name but really you should follow @KarlReid's advice and just use a return value. — Bergi
– Bergi, Commented Sep 26, 2017 at 16:19
@KarlReid: Everything is "pass by value". Only because objects are reference-type values doesn't mean they are "pass by reference". "Pass by reference" means this: var a = {}; var b = a; b = {}; console.log(a === b); /*this is not true in JavaScript*/ . What's the difference between passing by reference vs. passing by value? — Felix Kling
– Felix Kling, Commented Sep 26, 2017 at 16:20

llama · Accepted Answer · 2017-09-26 16:17:57Z

No, you only pass values, not variable references or pointers.

For that simple example, returning would seem more appropriate.

var works;
function create_gauge(id,  min,  max,  title,  label) {
  return new JustGage({
    id: id,
    value: 0,
    min: min,
    max: max,
    donut: false,
    gaugeWidthScale: 0.3,
    counter: true,
    hideInnerShadow: true,
    title: title,
    label: label,
    decimals: 2
  });
}
works = create_gauge("g2", 0, 100, "Füllstand", "%");
console.log(works);

However, I'm sure this is probably overly simplified. There are "reference types" in JS, so if works held an object, you could pass the value of the object reference and have the function populate a property of the object.

var works = {};
function create_gauge(obj, id,  min,  max,  title,  label) {
  obj.data = new JustGage({
    id: id,
    value: 0,
    min: min,
    max: max,
    donut: false,
    gaugeWidthScale: 0.3,
    counter: true,
    hideInnerShadow: true,
    title: title,
    label: label,
    decimals: 2
  });
}
create_gauge(works, "g2", 0, 100, "Füllstand", "%");
console.log(works.data);

Collectives™ on Stack Overflow

Javascript Function Global Variable undefined?

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related