3746273eda
* Path#ensureBlock keeps path context
This ensures that if you're inside an ArrowFunction with an expression body (say, you're on the BooleanLiteral in `() => true`), you don't suddenly lose your path context after inserting a variable.
This is because of 82d8aded8e (diff-9e0668ad44535be897b934e7077ecea5R14). Basically, an innocent `Scope#push` caused my visitor to suddenly stop working. Now, we mutate the Path so it's still in the tree.
* Tests
babel-plugin-transform-es2015-parameters
Compile ES2015 default and rest parameters to ES5
This plugin transforms ES2015 parameters to ES5, this includes:
- Destructuring parameters
- Default parameters
- Rest parameters
Examples
In
function test(x = "hello", { a, b }, ...args) {
console.log(x, a, b, args);
}
Out
function test() {
var x = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : "hello";
var _ref = arguments[1];
var a = _ref.a,
b = _ref.b;
for (var _len = arguments.length, args = Array(_len > 2 ? _len - 2 : 0), _key = 2; _key < _len; _key++) {
args[_key - 2] = arguments[_key];
}
console.log(x, a, b, args);
}
Installation
npm install --save-dev babel-plugin-transform-es2015-parameters
Caveats
Default parameters desugar into let declarations to retain proper semantics. If this is
not supported in your environment then you'll need the
transform-block-scoping plugin.
Usage
Via .babelrc (Recommended)
.babelrc
{
"plugins": ["transform-es2015-parameters"]
}
Via CLI
babel --plugins transform-es2015-parameters script.js
Via Node API
require("babel-core").transform("code", {
plugins: ["transform-es2015-parameters"]
});
Options
loose
boolean, defaults to false.
In loose mode, parameters with default values will be counted into the arity of the function. This is not spec behavior where these parameters do not add to function arity.
The loose implementation is a more performant solution as JavaScript engines will fully optimize a function that doesn't reference arguments. Please do your own benchmarking and determine if this option is the right fit for your application.
// Spec behavior
function bar1 (arg1 = 1) {}
bar1.length // 0
// Loose mode
function bar1 (arg1 = 1) {}
bar1.length // 1