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@babel/runtime

@babel/runtime is a library that contains Babel modular runtime helpers.

Installationโ€‹

npm install --save @babel/runtime

See also: @babel/runtime-corejs2.

Usageโ€‹

This is meant to be used as a runtime dependency along with the Babel plugin @babel/plugin-transform-runtime. Please check out the documentation in that package for usage.

Whyโ€‹

Sometimes Babel may inject some code in the output that is the same across files, and thus can be potentially re-used.

For example, with the class transform (without loose mode):

JavaScript
class Circle {}

turns into:

JavaScript
function _classCallCheck(instance, Constructor) {
  //...
}

var Circle = function Circle() {
  _classCallCheck(this, Circle);
};

this means every file that contains a class would have the _classCallCheck function repeated each time.

With @babel/plugin-transform-runtime, it would replace the reference to the function to the @babel/runtime version.

JavaScript
var _classCallCheck = require("@babel/runtime/helpers/classCallCheck");

var Circle = function Circle() {
  _classCallCheck(this, Circle);
};

@babel/runtime is just the package that contains the implementations of the functions in a modular way.