Tern

http://ternjs.net

Language challenges

Soundness?

eval(prompt("What next?"))

SpiderMonkey's inference algorithm

“Fast and Precise Hybrid
Type Inference
for JavaScript”

http://rfrn.org/~shu/drafts/ti.pdf

build

graph

capturing the

flow

of types

var x = "foo" // x :: string

var y = x     // y :: string

var x = "foo" // x :: string | bool
if (something()) x = false
var y = x     // y :: string | bool

var x = "foo"

var y = x

var x = "foo"
if (bar()) x = false
var y = x

var r = f("foo", "bar")
function f(x, y) { return x + y }

var r = f("foo", "bar")

var r = f("foo", "bar")
function f(x, y) { return x + y }

var r = f("foo", "bar")
function f(x, y) { return x + y }

var r = f("foo", "bar")
function f(x, y) { return x + y }

var r = f("foo", "bar")
function f(x, y) { return x + y }

var r = f("foo", "bar")
function f(x, y) { return x + y }

var r = f("foo", "bar")
function f(x, y) { return x + y }

var r = f("foo", "bar")
function f(x, y) { return x + y }

var o = {x: 10, y: 0}

var o = {x: 10, y: 0}
var h = o.y

var o = {x: 10, y: 0}
var h = o.y

Parametric Polymorphism

function lastOf(array) {
  return array[array.length - 1]
}

var num = lastOf([1, 2, 3])
var str = lastOf(["a", "b", "c"])

Run-time type manipulation

function extend(target, source) {
  for (var prop in source)
    target[prop] = source[prop]
  return target
}

Guessing

For Emacs, Vim, & ST

➤ install editor plug-in

➤ add .tern-project file

➤ go

Related Work

.Fin.

ternjs.net
github.com/marijnh/tern

marijnhaverbeke.nl
twitter.com/marijnjh