Question: Next example in VS2017 reported error: Property 'keys' does not exist on type 'any []'

```
[].keys()

```

Why error?

Version of Visual Studio 2017 - 15.6.4

Version of TypeScript tools - 15.6.20202.3

Version of TypeScript - 2.8

Answer: 
The problem fixed after tsconfig.json changing.

tsconfig.json

```
"compilerOptions": {
  ..
  "lib":["es2015"]
  ..
}

```
"esnext" works for me when used in tsconfig.json. Using VS Code