Convert to JSON with comments from PowerShell

Here you have an example which can't be handled right by previous answers:

{
"url":"http://something" // note the double slash in URL
}

so here is regexp that solves also this problem.

$configFile = $configFile -replace '(?m)(?<=^([^"]|"[^"]*")*)//.*' -replace '(?ms)/\*.*?\*/'

IMPORTANT NOTE:

Powershell 6.0+ can load JSON with comments in it.

Remove comment lines from your input before the conversion:

(Get-Content $JsonName) -replace '^\s*//.*' | Out-String | ConvertFrom-Json

The solution in the other answer only removes // comments if they are at the beginning of a line (with or without spaces), and doesn't remove /* multiline comments */

This code removes all kind of // and /* multiline comments *//

$configFile = (Get-Content path-to-jsonc-file -raw)
# Keep reading, for an improvement
# $configFile = $configFile -replace '(?m)\s*//.*?$' -replace '(?ms)/\*.*?\*/'

As @Jiří Herník indicates in his answer, this expression doesn't have into account the case of strings with comments inside it, for example "url": "http://mydomian.com". To handle this case:

$configFile = $configFile -replace '(?m)(?<=^([^"]|"[^"]*")*)//.*' -replace '(?ms)/\*.*?\*/'

for example removing the comments in this file:

{
  // https://github.com/serilog/serilog-settings-configuration
  "Serilog": {
    "MinimumLevel": "Error", // Verbose, Debug, Information, Warning, Error or Fatal
    "WriteTo": [
      {
        "Name": "File",
        "Args": {
          "path": "D:\\temp\\MyService\\log.txt",
          "rollingInterval": "Day",
          "outputTemplate": "{Timestamp:yyyy-MM-dd HH:mm:ss.fff zzz} [{Level:u3}] ({App}) ({Environment}) {Message:lj}{NewLine}{Exception}"
        }
      },
      {/*
        "Name": "Seq",*/
        "Args": {
          "serverUrl": "http://localhost:5341"
        }
      }
    ]
  }
}

results in:

{

  "Serilog": {
    "MinimumLevel": "Error",
    "WriteTo": [
      {
        "Name": "File",
        "Args": {
          "path": "D:\\temp\\MyService\\log.txt",
          "rollingInterval": "Day",
          "outputTemplate": "{Timestamp:yyyy-MM-dd HH:mm:ss.fff zzz} [{Level:u3}] ({App}) ({Environment}) {Message:lj}{NewLine}{Exception}"
        }
      } ,
      {
        "Args": {
          "serverUrl": "http://localhost:5341"
        }
      }
    ]
  }
}