Function can have an expression as a body?

[jamestalmage]

// core.js
def("Function")
    .bases("Node")
    .field("id", or(def("Identifier"), null), defaults["null"])
    .field("params", [def("Pattern")])
    .field("body", or(def("BlockStatement"), def("Expression")));

What would an ES5 function without a block statement look like? Is this just here to support arrow functions in ES6? If so, wouldn't it be better to override it in es6.js?

[benjamn]

Yep, that's left over from the original Mozilla Parser API (see the note). It's actually still possible (in SpiderMonkey) to write function increment(x) x + 1.

[jamestalmage]

interesting.

This works:

var ast = b.functionDeclaration(
  b.identifier('increment'),
  [b.identifier('x')],
  b.binaryExpression(
    '+',
    b.identifier('x'),
    b.literal(1)
  )
);

But if you try to print it it throws.

[jamestalmage]

Esprima seems to throw an error when parsing function increment(x) x + 1 anyways.