NG8101: Invalid Banana-in-Box

Description

This diagnostic detects a backwards "banana-in-box" syntax for two-way bindings.

<div ([var])="otherVar"></div>

What's wrong with that?

As it stands, ([var]) is actually an event binding with the name [var]. The author likely intended this as a two-way binding to a variable named var but, as written, this binding has no effect.

What should I do instead?

Fix the typo. As the name suggests, the banana ( should go inside the box []. In this case:

<div [(var)]="otherVar"></div>

Configuration requirements

strictTemplates must be enabled for any extended diagnostic to emit. invalidBananaInBox has no additional requirements beyond strictTemplates.

What if I can't avoid this?

This diagnostic can be disabled by editing the project's tsconfig.json file:

{
  "angularCompilerOptions": {
    "extendedDiagnostics": {
      "checks": {
        "invalidBananaInBox": "suppress"
      }
    }
  }
}

See extended diagnostic configuration for more info.