@gqlts/cli/src/render/typeGuards/renderTypeGuards.ts

Generate a client sdk from your GraphQl API

import { RenderContext } from '../common/RenderContext';
import { excludedTypes } from '../common/excludedTypes';
import { GraphQLSchema, isInterfaceType, isObjectType, isUnionType } from 'graphql';

const renderTypeGuard = (target: string, possible: string[], mode) =>
  mode == 'ts'
    ? `
const ${target}_possibleTypes: string[] = [${possible.map((t) => `'${t}'`).join(',')}]
export const is${target} = (obj?: { __typename?: any } | null): obj is ${target} => {
  if (!obj?.__typename) throw new Error('__typename is missing in "is${target}"')
  return ${target}_possibleTypes.includes(obj.__typename)
}
`
    : `
var ${target}_possibleTypes = [${possible.map((t) => `'${t}'`).join(',')}]
${mode === 'esm' ? 'export var ' : 'module.exports.'}is${target} = function(obj) {
  if (!obj || !obj.__typename) throw new Error('__typename is missing in "is${target}"')
  return ${target}_possibleTypes.includes(obj.__typename)
}
`;

export function renderTypeGuards(schema: GraphQLSchema, ctx: RenderContext, isJs: 'ts' | 'esm' | 'cjs' = 'ts') {
  const typeMap = schema.getTypeMap();
  for (const name in typeMap) {
    if (excludedTypes.includes(name)) continue;

    const type = typeMap[name];

    if (isUnionType(type)) {
      const types = type.getTypes().map((t) => t.name);
      ctx.addCodeBlock(renderTypeGuard(type.name, types, isJs));
    } else if (isInterfaceType(type)) {
      const types = schema.getPossibleTypes(type).map((t) => t.name);
      ctx.addCodeBlock(renderTypeGuard(type.name, types, isJs));
    } else if (isObjectType(type)) {
      ctx.addCodeBlock(renderTypeGuard(type.name, [type.name], isJs));
    }
  }
}