Meta Model for TypeScript and EcmaScript apps, to help with JSON schema processing and UI construction.


Keywords
model, driven, metamodel
License
MIT
Install
npm install @hn3000/metamodel@1.9.0

Documentation

Meta Model for JavaScript Apps

Coming from statically typed languages like Pascal, C and C++, I always wanted to have more strict typings for my JavaScript classes. While TypeScript allows me to describe the data using interfaces, I feel it lacks RTTI -- runtime information about the objects involved that would allow me to construct user interfaces dynamically and validate incoming data (either from some remote connection or typed in by a user) against the type information.

This is my attempt at building something to fill this gap.

A metamodel is created like this:

var sampleObject = {
    lala: 12,
    blah: "Some String",
    blub: 3.1415 * 12
};

var modelTypes = require("metamodel").modelTypes;

var model = modelTypes.addObjectType('sample')
  .addItem('lala', modelTypes.type('number/int'))
  .addItem('blah', modelTypes.type('string'))
  .addItem('blub', modelTypes.type('number'));

Once the model exists it in the modelTypes registry, it can always be referred to by name:

var model = modelTypes.type('sample');

And input data can be validated by the model:

var inputData = {
    lala: "12",
    blah: "Another String",
    blub: 27.12
};

var context = modelTypes.createParseContext(inputData, model);
context.allowConversion = true;
model.validate(context);
if (context.warnings.length) {
    console.warn(`context.messages.map(e => e.msg).join(', ')`);
}
if (context.errors.length) {
    console.error(`context.errors.map(e => e.msg).join(', ')`);
    throw new Error('Validation failed');
}

At this point, context will contain warnings and errors if the data does not fit the metamodel. With allowConversion=true, the metamodel will parse "12" into a number, if allowConversion=false, the string value will result in an error message.