Ts-jest: Understanding how ts-jest works

[ahnpnl]

• Issue
  An open topic to get to understand how ts-jest works

• Expected behavior
  N.A.

• Output from your debug log
  N.A.

• Link to a minimal repo that reproduces this issue
  N.A.

• Optional (but highly recommended) - Configure Travis (or your favorite system) with the minimal repo
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I have some following questions regarding to how ts-jest works:

• How does it work ?
• Why do we need babel ?
• What is the relationship between babel and tsc ?
• How can I check the transpiled codes ? The transpiled codes are the codes passing to Jest ?
• Debugging process for ts-jest: Where should I start ? How can I enable logging to debug ts-jest ?

If anyone else has other questions, we can discuss it here.

[kulshekhar]

How does it work ?

In a nutshell,

• jest calls the process function in ts-jest with the source code (once for each matched file) and configuration
• ts-jest returns the transpiled source code + sourcemaps back to jest

Why do we need babel ?

to support hoisting

What is the relationship between babel and tsc ?

There is no direct relationship between babel and tsc

How can I check the transpiled codes ? The transpiled codes are the codes passing to Jest ?

The transpiled code is returned to jest. To check the transpiled code, you'll have to put a log statement in node_modules/ts-jest/dist/preprocessor.js in the correct location

Debugging process for ts-jest: Where should I start ? How can I enable logging to debug ts-jest ?

by setting the TS_JEST_DEBUG env variable to true

[kulshekhar]

I'm closing this issue but this discussion can continue.