Issue
I was reading Nats-Jetstream documentation that I encountered the following code:
var createModel = require('jetstream').model;
var Shape = createModel('Shape', function() {
this.has('x', Number);
this.has('y', Number);
this.has('width', Number);
this.has('height', Number);
this.has('type', Number);
});
I am not sure what does this.has mean? Where does the has come from? How does this code work?
Solution
The shape of the library is described in the docs. It has:
type JetStream : {
model: (name: String, fn: ModelDefiner) => Model,
So the callback is a ModelDefiner, which is defined here:
type ModelDefiner : (this: Model) => void
So this is a Model, which is defined here:
type ModelObject : {
has: (propertyName: String, PropertyType) => void,
setScope: (scope: Scope, Callback<Error, void>) => void,
getValues: () => Object,
getAddSyncFragment: () => SyncFragment<"add">
}
-- A Model instance inherits from ModelObject.
type Model : ModelObject & {
typeName: String,
uuid: ObjectUUID,
scope: Scope | null
}
As you can see above, a Model extends a ModelObject, and a ModelObject has a has method.
If you're curious how you would write code that could do this yourself, all you really need is to create an object with a has method, and .call the callback with it.
class Model {
has(str, type) {
console.log('has called with', str, type);
};
}
const createModel = (str, callback) => {
const model = new Model();
callback.call(model);
};
var Shape = createModel('Shape', function() {
this.has('x', Number);
this.has('y', Number);
this.has('width', Number);
this.has('height', Number);
this.has('type', Number);
});Answered By - CertainPerformance Answer Checked By - Terry (PHPFixing Volunteer)
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