IE11 errors on main.js because of `const` in `for (const ...`

• I have searched the issues of this repository and believe that this is not a duplicate.

Expected Behavior

Next deployments should work in IE11.

Current Behavior

My Next deployment does not work in IE11.

The error is

SCRIPT1053: Const must be initialized
File: main.s, Line: 1, Column 503674

I looked at that place in main.js, which has this snippet–

... for(const e of Object.keys(o)) ...

I looked online, and apparently IE11 doesn’t allow const or let in for loops, like for (const var ....

I removed all these for (const and for (let forms from my code and redeployed, but got the same result. I believe it’s because there are 9 modules in my node_modules that use the for (const ... form. I can’t replace these modules.

Is there some way to have next build the code and convert these for (const and for (let forms to for (var or for (... so I can support IE11?

I am using Typescript, but I don’t think that should make a difference.

Steps to Reproduce (for bugs)

Deploy any code with a for (const loop in it.

Your Environment

Tech	Version
next	5.1.0
node	9.8.0
browser	IE version 11.0.9600.18860

[omeraplak]

@kedarguy @tashburn i add babel polyfill to my project and fixed all.

This my setup;

.babelrc

"presets": [
		[
			"next/babel",
			{
				"preset-env": {
					"targets": {
						"browsers": [
							"IE >= 11"
						]
					},
					"useBuiltIns": "entry"
				}
			}
		]
	]

pages/_document.js

import '@babel/polyfill'

next.config.js

webpack: (config, { dev, isServer }) => {
        const originalEntry = config.entry;
	config.entry = async () => {
	const entries = await originalEntry()
	if (entries['main.js'].indexOf("@babel/polyfill") === -1) {
		entries['main.js'].unshift("@babel/polyfill")
	}
	return entries
	}
});

npm i --save @babel/polyfill

[timneutkens]

Going to close based on @oliviertassinari’s comment.

It’d be tremendously helpful if you provide full steps to reproduce when creating issues, otherwise it takes more time than it should to check out particular issues. Thanks 🙏