demo/typescript.js
function getTypeFromTypeAliasReference(node, symbol) {
            var type = getDeclaredTypeOfSymbol(symbol);
            var links = getSymbolLinks(symbol);
            var typeParameters = links.typeParameters;
            if (typeParameters) {
                if (!node.typeArguments || node.typeArguments.length !== typeParameters.length) {
                    error(node, ts.Diagnostics.Generic_type_0_requires_1_type_argument_s, symbolToString(symbol), typeParameters.length);
                    return unknownType;
                }
                var typeArguments = ts.map(node.typeArguments, getTypeFromTypeNode);
                var id = getTypeListId(typeArguments);
                return links.instantiations[id] || (links.instantiations[id] = instantiateType(type, createTypeMapper(typeParameters, typeArguments)));
            }
            if (node.typeArguments) {
                error(node, ts.Diagnostics.Type_0_is_not_generic, symbolToString(symbol));
                return unknownType;
            }
            return type;
        }
function getTypeFromTypeAliasReference(node, symbol) {
            var type = getDeclaredTypeOfSymbol(symbol);
            var links = getSymbolLinks(symbol);
            var typeParameters = links.typeParameters;
            if (typeParameters) {
                if (!node.typeArguments || node.typeArguments.length !== typeParameters.length) {
                    error(node, ts.Diagnostics.Generic_type_0_requires_1_type_argument_s, symbolToString(symbol), typeParameters.length);
                    return unknownType;
                }
                var typeArguments = ts.map(node.typeArguments, getTypeFromTypeNode);
                var id = getTypeListId(typeArguments);
                return links.instantiations[id] || (links.instantiations[id] = instantiateType(type, createTypeMapper(typeParameters, typeArguments)));
            }
            if (node.typeArguments) {
                error(node, ts.Diagnostics.Type_0_is_not_generic, symbolToString(symbol));
                return unknownType;
            }
            return type;
        }
Get type from reference to type alias. When a type alias is generic, the declared type of the type alias may include references to the type parameters of the alias. We replace those with the actual type arguments by instantiating the declared type. Instantiations are cached using the type identities of the type arguments as the key.