pxt-calliope/editor/tsconfig.json

{
    "compilerOptions": {
        "target": "es2017",
        "noImplicitAny": true,
        "noImplicitReturns": true,
        "noImplicitThis": true,
        "declaration": true,
        "module": "commonjs",
        "moduleResolution": "node",
        "isolatedModules": false,
        "outDir": "../built/editor",
        "rootDir": ".",
        "newLine": "LF",
        "sourceMap": false,
        "jsx": "react",
        "lib": [
            "dom",
            "dom.iterable",
            "scripthost",
            "es2017",
            "ES2018.Promise"
        ]
    }
}