karma-typescript-es6-transform: Fixing preset problem after upgrading

FixingPresetProblemAfterUpgrading.md

Recently, I upgraded the devDependencies in one of my projects to the current versions. This included an update of karma-typescript-es6-transform from version 1.0.2 to 1.0.3. Didn't sound dangorous. But afterwards my tests didn't run by karma any more.

Update 25-Feb-2018: with the latest version 1.0.4 of karma-typescript-es6-transform the error doesn't occur anymore.

I just got:

18 02 2018 11:20:49.774:ERROR [karma]: Error: .../ionic-logging-service/node_modules/ionic-configuration-service/dist/index.js: Couldn't find preset "es2015" relative to directory ".../ionic-logging-service/node_modules/ionic-configuration-service/dist"
Transform function:

function (context, callback) {
        if (!context.js) {
            return callback(undefined, false);
        }
        if (isEs6(context.js.ast)) {
            options.filename = context.filename;
            log.debug("Transforming %s", options.filename);
            try {
                context.source = babel.transform(context.source, options).code;
                context.js.ast = acorn.parse(context.source, { sourceType: "module" });
                return callback(undefined, true);
            }
            catch (error) {
                return callback(error, false);
            }
        }
        else {
            return callback(undefined, false);
        }
    }

    at Transformer.handleError (.../ionic-logging-service/node_modules/karma-typescript/dist/bundler/transformer.js:108:19)
    at .../ionic-logging-service/node_modules/karma-typescript/dist/bundler/transformer.js:89:27
    at transform (.../ionic-logging-service/node_modules/karma-typescript-es6-transform/dist/transform.js:57:24)
    at .../ionic-logging-service/node_modules/karma-typescript/dist/bundler/transformer.js:83:17
    at _combinedTickCallback (internal/process/next_tick.js:73:7)
    at process._tickCallback (internal/process/next_tick.js:104:9)

The most results on Google told me this were a problem that the newer versions of babel would use babel-preset-env instead of babel-preset-es2015. Apparently, something wanted to use the later one, but in my installed node modules was only babel-preset-env, which is a dependency to karma-typescript-es6-transform@1.0.3.

So I came up with 2 solutions:

• install babel-preset-es2015 manually
• tell babel to use babel-preset-env

I preferred the second solution. Therefore I added to my karma.conf.js the option:

karmaTypescriptConfig: {
  bundlerOptions: {
    transforms: [
      require("karma-typescript-es6-transform")({
        presets: [
          ["env"]
        ]
      })
    ]
  }
},

As often, it is enough to write a few characters to solve a problem. You only need to know the characters and the right place...

If you are interested in the whole solution, have a look a the aforementioned project.