optional-chain.md

Babel.js AST for obj?.foo.bar

It looks strange to me the decision to consider all the chain (dots) as the type OptionalMemberExpression and not just the first one

{
  "type": "File",
    "program": {
    "type": "Program",
    "body": [
      {
        "type": "ExpressionStatement",
        "expression": {
          "type": "OptionalMemberExpression",
          "object": {
            "type": "OptionalMemberExpression",
            "object": {
              "type": "Identifier",
              "name": "obj"
            },
            "computed": false,
            "property": {
              "type": "Identifier",
              "name": "foo"
            },
            "optional": true
          },
          "computed": false,
          "property": {
            "type": "Identifier",
            "name": "bar"
          },
          "optional": false
        }
      }
    ]
  }
}

Espree AST for obj?.foo.bar

Curiously the AST produced by Babel.js is different from the one produced by Espree. The OptionalMemberExpression node is not present in the Espree AST. Instead, the ChainExpression node is used to represent the optional chaining operation. It appears a ChainExpression node followed by the inners MemberExpression nodes. The optional property has the same behavior.

➜ babel-learning git:(main) ✗ compast -lp 'obj?.foo.bar'

type: "Program"
body:
  - type: "ExpressionStatement"
    expression:
      type: "ChainExpression"
      expression:
        type: "MemberExpression"
        object:
          type: "MemberExpression"
          object:
            type: "Identifier"
            name: "obj"
          property:
            type: "Identifier"
            name: "foo"
          computed: false
          optional: true
        property:
          type: "Identifier"
          name: "bar"
        computed: false
        optional: false
sourceType: "module"