SyntaxError: Unexpected keyword 'const'. Const declarations are not supported in strict mode.

I use webpack@4.28.4 and babel@7.2.0 in my project.

{
	"@babel/cli": "^7.2.0",
	"@babel/core": "^7.2.0",
	"@babel/plugin-proposal-class-properties": "^7.2.1",
	"@babel/plugin-proposal-decorators": "^7.3.0",
	"@babel/plugin-proposal-object-rest-spread": "^7.2.0",
	"@babel/plugin-syntax-dynamic-import": "^7.2.0",
	"@babel/plugin-proposal-optional-chaining": "7.2.0",
	"@babel/polyfill": "^7.2.5",
	"@babel/preset-env": "^7.2.0",
	"@babel/preset-react": "^7.0.0",
	"@babel/preset-typescript": "^7.1.0"
}

But the project can’t run in iPhone IOS9 Safari, it has a compile error:

The code that caused the error：

I tried to modify @babel/env to fix this error：

"presets": [
    [
      "@babel/env",
      {
        "useBuiltIns": "usage",
        "targets": {
          "chrome": 52,
          "browsers": ["last 2 versions", "safari 7"]
        },
        "loose": true
      }
    ]
  ],

but it is invalid…

I need a solution, please help me. (My English is not good, please forgive me.)

[gupnee81]

@Vibing - Could you please share webpack settings. I would like to refer them as I am facing same issue.

[simkessy]

Make sure you have the latest @babel/polyfill.

They introduced a bug that caused this error.

Run npm i @babel/polyfill@latest and it should fix the problem: https://github.com/babel/babel/pull/9812