Compile ES2015 block scoping (const and let) to ES5
npm install --save-dev babel-plugin-transform-es2015-block-scoping
babel --plugins transform-es2015-block-scoping script.js
In cases such as the following it's impossible to rewrite let/const without adding an additional function and closure while transforming:
for let i = 0; i < 5; i++;
In extremely performance-sensitive code, this can be undesirable. If
"throwIfClosureRequired": true is set, Babel throws when transforming these patterns instead of automatically adding an additional function.