A few years ago, I came up with a similar proposal, though more specifically aimed at making callbacks easier to manage. It was a simple syntax extension, as op

A few years ago, I came up with a similar proposal, though more specifically aimed at making callbacks easier to manage. It was a simple syntax extension, as opposed to new semantics for the language. You would write this: var! x = expression; statement; statement; And JavaScript would parse it as: return expression.then(function(x) { statement; statement; }); This is obviously shamelessly pilfered from monadic syntax 'let!' in F#, and my own 'let!' extension in OCaml.