Systems

Systems define how your entities interact with each other in the world, and use queries to modify specific entities' properties

Create a System

To create a system, use the System function to create a class and extend it to add your own methods:

class MyCustomSys extends System({}) {}

Queries

As mentioned in the queries page, the System() function takes a single argument: A Tree of query modifiers (or modifier shorthand). These then create a matching tree of queries that can be accessed inside the system's entities property:

class MyCustomSys extends System(With(ComponentA)) {
    update() {
        this.entities.forEach((ent) => console.log(ent.get(ComponentA)));
    }
}

Add a system to the world

To add a system to the world, you pass either the extended class or an instance to World.prototype.addSystem():

world.addSystem(new MyCustomSys());

// Can also use
world.addSystem(MyCustomSys);

This will also enable the system by default.

Enable a system:

To enable a system (call its update() method anytime the world is updated), use World.prototype.enable and pass in the class:

world.enable(MyCustomSys);

Disable a system:

There is no reason for a system to be fully removed from the world, but you can disable it from updating with the rest of the world using World.prototype.disable:

world.disable(MyCustomSys);

Update systems

World.prototype.update() is used to update the world, and can optionally take an array of System classes to update. If none are passed, all currently enabled systems are updated:

// Update all enabled systems
world.update();

// Update specific systems
world.update(MyCustomSysA, MyCustomSysB);

caution

When explicitly stating which systems to update, BagelECS doesn't check if a system is enabled or disabled. This means that if you are using your own enable/disable logic, and explicitly stating which systems to run, you could accidentally run a system after disabling it.