Question

What is the name of the technique the example uses below to pass a variable to an object in javascript? And furthermore, why is it not working (“large” is not outputted to the console log as expected)?

var thumbnailBlock = new ThumbnailBlock();
thumbnailBlock.thumbnailSize = "large";


function ThumbnailBlock() {

    this.thumbnailSize;

    console.log("DEBUG");
    console.log(this.thumbnailSize);
}

Answer 1

The explanation what is going wrong in your code from Willem Mulder’s answer:

There is no specific name. You simply set an object property.

The ‘large’ is not outputted because you first create an object using the ThumbnailBlock constructur function (where it logs the this.thumbnailSize) and only then set the .thumbnailSize to "large".

You could pass the size as function argument.

function ThumbnailBlock(size) {
    this.thumbnailSize = size;
}

var thumbnailBlock = new ThumbnailBlock("large");

console.log(thumbnailBlock.thumbnailSize);

Also, have a look at the The Constructor Pattern and other nice patterns on that page. I also recommend the chapter on OOP in the free book Eloquent JavaScript.