under-the-hood of type systems: type checks logic.js

const errors = [];

const ANNOTATED_TYPES = {
  NumberTypeAnnotation: "number",
  GenericTypeAnnotation: true
};

// Logic for type checks
const typeChecks = {
  expression: (declarationFullType, callerFullArg) => {
    switch (declarationFullType.typeAnnotation.type) {
      case "NumberTypeAnnotation":
        return callerFullArg.type === "NumericLiteral";
      case "GenericTypeAnnotation": // non-native
        // If called with Object, check properties
        if (callerFullArg.type === "ObjectExpression") {
          // Get Interface
          const interfaceNode = ast.program.body.find(
            node => node.type === "InterfaceDeclaration"
          );
          // Get properties
          const properties = interfaceNode.body.properties;

          // Check each property against caller
          properties.map((prop, index) => {
            const name = prop.key.name;
            const associatedName = callerFullArg.properties[index].key.name;
            if (name !== associatedName) {
              errors.push(
                `Property "${associatedName}" does not exist on interface "${interfaceNode.id.name}". Did you mean Property "${name}"?`
              );
            }
          });
        }
        return true; // as already logged
    }
  },
  annotationCheck: arg => {
    return !!ANNOTATED_TYPES[arg];
  }
};