Initializing a javascript object containing an array

Question

I have the following C++ struct which I want to create as faithfully as possible in Javascript:

struct Vertex
{
   float coords[4];
   float colors[4];
};

So I did the following:

function Vertex(coords, colors)
{
   this.coords = [];
   this.colors = [];
}

Now, the following works to create a Vertex instance:

var oneVertex = new Vertex();
oneVertex.coords = [20.0, 20.0, 0.0, 1.0];
oneVertex.colors = [0.0, 0.0, 0.0, 1.0];

but the following (slicker?) doesn't:

var oneVertex = new Vertex([20.0, 20.0, 0.0, 1.0], 
                            [0.0, 0.0, 0.0, 1.0]);

Why? I am new to Javascript and what little I have read suggests it should be ok. Obviously not. It would be helpful to understand what I am missing. Thanks.

you are passing the arrays to the function, but you are setting the coords and colors to empty and not using the data you pass in — user2950720
– user2950720, Commented Apr 17, 2016 at 20:48
There's a strong distinction between function parameters and object properties. Learning language basics is always a good start. — user1106925
– user1106925, Commented Apr 17, 2016 at 20:48

Sudhir Bastakoti · Accepted Answer · 2016-04-17 20:47:50Z

5

you need to use the arguments passed in to the function for it to work, as:

function Vertex(coords, colors)
{
   this.coords = coords || [];
   this.colors = colors || [];
}

answered Apr 17, 2016 at 20:47

Sudhir Bastakoti

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Comments

Ori Drori · Accepted Answer · 2016-04-17 20:47:10Z

1

You're constructor should initialize the properties:

function Vertex(coords, colors)
{
   this.coords = coords;
   this.colors = colors;
}

var oneVertex = new Vertex([20.0, 20.0, 0.0, 1.0], 
                            [0.0, 0.0, 0.0, 1.0]);

answered Apr 17, 2016 at 20:47

Ori Drori

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