Javascript OOP - Function within return function

Question

Trying to create function call that only be called if other function has been called within same line.

var processTrack = new function() {
    this.current = 1;
    this.max = 5800;
    this.min = 0;
    this.done = function(started, processing, cur, len) {
        cur = cur || 0;
        len = len || 1;
        var res = 0;
        if (started && !processing)
            res = ((this.current - 1 - this.min) / (this.max - this.min)).toFixed(2);
        else if (!started && processing)
            res = (this.done(true, false) + (this.step() * this.cur / this.len)).toFixed(2);
        else if (!started && !processing)
            res = ((++this.current - 1 - this.min) / (this.max - this.min)).toFixed(2);

        this.percentage = function() {
            return res * 100 + "%";
        };
        return res;
    };
    this.step = function() {
        return 1 / (this.max - this.min);
    };
}

What I ideally want is to call processTrack.done(args).percentage() to get percentage from the data I recieved from .done(args), but whenever I try to call (for example) processTrack.done(true, false).percentage() it gives me an error saying:

TypeError: processTrack.done(...).percentage is not a function

What am I doing wrong?

You're trying to call .percentage() on res, not on this.done. Try doing res.percentage = function() ...; return res;. — David Ehrmann
– David Ehrmann, Commented Jul 17, 2015 at 22:56
But really, rethink this a bit. You probably don't want to put presentation logic in the function tracking progress. — David Ehrmann
– David Ehrmann, Commented Jul 17, 2015 at 22:57
Why processTrack = new function()? You can do processTrack = function() {} and use variables inside function scope, exposing only an object returned by the function. — Félix
– Félix, Commented Jul 17, 2015 at 22:59

Maximillian Laumeister · Accepted Answer · 2015-07-17 22:57:20Z

2

You need to return this instead of res at the end of your this.done function. By returning this, you are returning your this.done function, which is the object that has the percentage function in it.

The following code runs without errors:

var processTrack = new function() {
    this.current = 1;
    this.max = 5800;
    this.min = 0;
    this.done = function(started, processing, cur, len) {
        cur = cur || 0;
        len = len || 1;
        var res = 0;
        if (started && !processing)
            res = ((this.current - 1 - this.min) / (this.max - this.min)).toFixed(2);
        else if (!started && processing)
            res = (this.done(true, false) + (this.step() * this.cur / this.len)).toFixed(2);
        else if (!started && !processing)
            res = ((++this.current - 1 - this.min) / (this.max - this.min)).toFixed(2);

        this.percentage = function() {
            return res * 100 + "%";
        };
        return this;
    };
    this.step = function() {
        return 1 / (this.max - this.min);
    };
}

processTrack.done(true, false).percentage();

answered Jul 17, 2015 at 22:57

Maximillian Laumeister

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1 Comment

Confuseh Over a year ago

Ah, so that was the problem. Thanks.

abs · Accepted Answer · 2015-07-17 23:02:01Z

1

Return this in done method. As it is returning res which is not an object

answered Jul 17, 2015 at 23:02

abs

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