@babel/plugin-transform-block-scoping
Advanced tools
Package description
The @babel/plugin-transform-block-scoping npm package is a Babel plugin that transforms JavaScript code to convert block scoping (let and const) to function scoping (var) where necessary. This is particularly useful for ensuring compatibility with older environments that do not support ES6 block-scoped variables.
Transform let and const to var
This feature transforms block-scoped variables (let and const) into function-scoped variables (var) to ensure compatibility with older JavaScript engines.
if (true) {
let x = 'hello';
}
// Transformed to:
if (true) {
var x = 'hello';
}Block scoping for loops
This feature correctly scopes the loop variable within closures, preventing common errors when using setTimeout or similar asynchronous functions within loops.
for (let i = 0; i < 3; i++) {
setTimeout(function() { console.log(i); }, 0);
}
// Transformed to:
for (var i = 0; i < 3; i++) {
(function(i) {
setTimeout(function() { console.log(i); }, 0);
})(i);
}This package is a predecessor to @babel/plugin-transform-block-scoping and offers similar functionality, transforming ES2015 block-scoped variables to ES5. It is now deprecated in favor of the @babel suite of plugins.
While not a direct alternative, fast-async is a Babel plugin that transforms async/await and generators to ES5, including handling block scoping within async functions. It provides a different set of features but deals with modern JavaScript syntax transformation like @babel/plugin-transform-block-scoping.
babel-preset-env is a Babel preset that includes @babel/plugin-transform-block-scoping among other plugins. It automatically determines the Babel plugins and polyfills you need based on your supported environments. It's a more comprehensive solution that includes similar functionality.
Readme
Compile ES2015 block scoping (const and let) to ES5
In
{
let a = 3
}
let a = 3
Out
{
var _a = 3;
}
var a = 3;
npm install --save-dev @babel/plugin-transform-block-scoping
.babelrc (Recommended).babelrc
Without options:
{
"plugins": ["@babel/plugin-transform-block-scoping"]
}
With options:
{
"plugins": [
["@babel/plugin-transform-block-scoping", {
"throwIfClosureRequired": true
}]
]
}
babel --plugins @babel/plugin-transform-block-scoping script.js
require("@babel/core").transform("code", {
plugins: ["@babel/plugin-transform-block-scoping"]
});
throwIfClosureRequiredIn 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++) {
setTimeout(() => console.log(i), 1);
}
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.
FAQs
Compile ES2015 block scoping (const and let) to ES5
The npm package @babel/plugin-transform-block-scoping receives a total of 19,372,637 weekly downloads. As such, @babel/plugin-transform-block-scoping popularity was classified as popular.
We found that @babel/plugin-transform-block-scoping demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 4 open source maintainers collaborating on the project.
Did you know?
Socket for GitHub automatically highlights issues in each pull request and monitors the health of all your open source dependencies. Discover the contents of your packages and block harmful activity before you install or update your dependencies.
Security News
The JavaScript community has launched the e18e initiative to improve ecosystem performance by cleaning up dependency trees, speeding up critical parts of the ecosystem, and documenting lighter alternatives to established tools.
Product
Socket now supports four distinct alert actions instead of the previous two, and alert triaging allows users to override the actions taken for all individual alerts.
Security News
Polyfill.io has been serving malware for months via its CDN, after the project's open source maintainer sold the service to a company based in China.