Skip _extends helper for {…x} with modern targets

[nicolo-ribaudo]

Q	A
Fixed Issues?
Patch: Bug Fix?
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

The _extends helper already delegates to Object.assign when it is available.
If we statically know that Object.assign exists (using the user's targets), we can avoid injecting _extends.

[nicolo-ribaudo]

Without this PR, the output would be something like

function _extends() { _extends = Object.assign || function (target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i]; for (var key in source) { if (Object.prototype.hasOwnProperty.call(source, key)) { target[key] = source[key]; } } } return target; }; return _extends.apply(this, arguments); }

let a = _extends({
  x: 1
}, b);

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/42582/

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[JLHwung]

The future is on the horizon: preset-env will be simplified to a static array of babel plugins.

[nicolo-ribaudo]

Yes! 😄

[existentialism]

💯