He said, She said, They Said, Who Said?

This topic is about the "Power Struggle" inside the code. When a block is born, it needs to know what its data is. LegoDOM looks at three different places to find that data, and it has a strict hierarchy of who wins in a conflict.

Diffing, Merging, and Priorities (The Tier System)

Inside the snap(el) function, you will see a variable called logic. This isn't just a simple object; it is the result of a three-way merge. The code uses the spread operator { ... } to layer these "Tiers."

The Three Tiers of Authority

1. Tier 1: The Global Definition (Lowest Priority)

   const baseLogic = legoFileLogic.get(name) || {};

   This is the JavaScript object you provided when you called Lego.block(). It contains your default values and methods. It’s the "fallback" data. Lego Files and .lego blocks fall under this tier.

2. Tier 2: The Template Attributes (Middle Priority)

   const templateLogic = parseJSObject(t.getAttribute('b-data')) || {};

   Lego looks at the <template> tag itself in your HTML. If you added a b-data attribute there, it overrides the global definition. This is useful for creating "variants" of a block template without writing new JavaScript.

3. Tier 3: The Instance Attributes (Highest Priority)

   const instanceLogic = parseJSObject(el.getAttribute('b-data')) || {};

   This is the data attached to the specific tag on your page (e.g., <user-profile b-data="{id: 42}">). This is the "Final Word." If the instance says the ID is 42, it doesn't matter what the template or the global definition said.

The Merge Order

The code combines them like this:

JavaScript

const mergedLogic = { ...baseLogic, ...templateLogic, ...instanceLogic };

In JavaScript, when you spread objects, the properties on the right overwrite properties on the left. So, Instance > Template > Definition.

The parseJSObject Utility

To make this work, LegoDOM includes a helper called parseJSObject.

• Why not JSON.parse? JSON is strict (requires double quotes, no functions).

• LegoDOM's Way: It uses new Function('return ' + str)(). This is a powerful (and dangerous) trick that allows you to write actual JavaScript inside your HTML attributes, including functions or arrays, which Lego then evaluates into a real object.

The Edge Case: b-data as a "Ref"

If the b-data attribute starts with a $, like b-data="$someGlobal", LegoDOM treats it as a pointer to a global variable instead of a raw object string. This allows for deep data sharing between the block and the outside world.

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Summary: A block's data is a "Cake" with three layers. The Global Logic is the bottom, the Template Logic is the middle, and the Instance Logic is the frosting. The "Frosting" (Instance) is what the user ultimately sees.