Force ES5 for TS compilation

[lmiller1990]

This prevents const vue_1 = require('vue') from conflicting, since it will do var vue_1 instead.

This feels pretty bad, I don't know the correct solution. 🤔

[LinusBorg]

I think we could use a pretty basic regex to change that line to a var ... somewhere around here:

vue-jest/lib/generate-code.js

Lines 22 to 25 in e0cbca7

	if (output.includes('exports.render = render;')) {
	output += ';exports.default = {...exports.default, render};'
	} else {
	output += ';exports.default = {...exports.default};'

[LinusBorg]

This whole part is a bit brittle since we use code that is meant to end up in multiple (virtual) files and concat it into one piece of code.

If I were to have a top-level variable or function called render in my script block, the function render( generated by the template compilation step would conflict here as well, I would assume.

[lmiller1990]

I would say so - I experimented a bit to try and get other variables to conflict, no luck, but I'm sure it's possible.

I am not really sure on the best way to solve this problem 🤔 Maybe we need some way to hoist up the common imports and do not duplicate them. That would not solve the top level render conflict you pointed out, though. I pinged a maintainer of ts-jest to get some ideas, he may have some experience around this.

Edit: he suggests asking the babel team: #238 (comment). I will play around a little more and see if I can think of a better approach.

[ahnpnl]

Hi, come back to this I have a suspicion. It seems like the error is thrown because in the final js output which is given to jest containing twice const vue_1 = require(‘vue’) which will then cause the issue cannot redeclare block-scope variable.

If that is the case, the const vue_1 = require(‘vue’) needs to be removed from vue-jest transpile output by either of these ways:

• Use regex
• Write a Babel plug-in, which is also an AST transformer to use with Babel.
• Write a TypeScript transformer, which is also AST transformer to use with TypeScript API.

I’d recommend to use AST transformer over regex when dealing with transpiling codes

[lmiller1990]

I think you are right - using var is just a work around, not really a good solution.

I think that we should make a new codebase for a TypeScript and ts-jest based solution that implements the best patterns that I learned from looking at other jest transformers, and pin it to Jest versions like ts-jest does - supports both Vue 2.x and 3.x, and multiple jest versions, is very difficult in a single codebase.

[ahnpnl]

ya, agree. Maybe you can setup the base structure 1st and others can start contributing, also worth to write down in an issue about all the plans :)

[lmiller1990]

Yep, we definitely need a good "plan of attack".