node.js - TypeScript compiler does not throw error on missing declaration -

i have found strange case in nodejs project. try describe problem here believing there's simple option in tsconfig.json case. use typescript v1.7.3.

file test1.ts contains variable declaration:

// test1.ts let = 1; 

file test2.ts contains improper variable usage:

// test2.ts console.log(a); 

tsconfig.json looks this:

// tsconfig.json {   "compileroptions": {     "module": "commonjs",     "target": "es5"   } } 

compiler not throw error me using undeclared variable a. if try export other variable, b expected error:

// test1.ts let = 1; export let b = 2; 

compiler:

error:(1, 13) ts2304: cannot find name 'a'. 

how can make compiler emit error in first case? i've found out in project removed variable , failed in runtime, not compile time.

this unfortunate consequence of fact files without kind of export or import considered "script" files compiler. compiler assumes script files operate in global scope, , stitched together. without --outfile being specified, won't able whether variable declaration occur after usage.

one workaround add a

export {}; 

statement files.