@babel/plugin-transform-parameters
Advanced tools
Package description
The @babel/plugin-transform-parameters package is a Babel plugin that transforms function parameter features, such as default parameters, destructured parameters, and rest parameters, into ES5-compatible syntax. This transformation allows developers to use modern JavaScript features while maintaining compatibility with older environments that may not support these newer syntaxes natively.
Default Parameters
Transforms functions with default parameters to check for `undefined` and assign a default value if necessary. This allows for cleaner function signatures and easier parameter handling.
function log(message = 'Default message') { console.log(message); }Destructured Parameters
Enables the use of destructuring in function parameters, transforming it into a series of variable assignments for compatibility. This simplifies the extraction of properties from objects passed as function arguments.
function greet({ name, age }) { console.log(`Hello ${name}, you are ${age} years old.`); }Rest Parameters
Transforms rest parameters into a standard ES5 arguments pattern, allowing functions to accept an indefinite number of arguments as an array.
function concatenate(separator, ...strings) { return strings.join(separator); }Similar to the destructuring aspect of @babel/plugin-transform-parameters, this plugin transforms destructuring assignments and rest/spread properties to ES5. However, it focuses more broadly on destructuring patterns outside of function parameters as well.
This plugin transforms spread elements into a form that can be understood by environments without native support for this syntax. While it deals with the spread operator like the rest parameters feature of @babel/plugin-transform-parameters, it's applied in array literals and function calls rather than function parameters.
Focuses specifically on transforming default parameters in functions to ES5 syntax, similar to one of the functionalities provided by @babel/plugin-transform-parameters. It offers a more targeted approach to handling default parameters.
Readme
Compile ES2015 default and rest parameters to ES5
This plugin transforms ES2015 parameters to ES5, this includes:
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);
}
npm install --save-dev @babel/plugin-transform-parameters
Default parameters desugar into let declarations to retain proper semantics. If this is
not supported in your environment then you'll need the
@babel/plugin-transform-block-scoping plugin.
.babelrc (Recommended).babelrc
{
"plugins": ["@babel/plugin-transform-parameters"]
}
babel --plugins @babel/plugin-transform-parameters script.js
require("@babel/core").transform("code", {
plugins: ["@babel/plugin-transform-parameters"]
});
looseboolean, 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
FAQs
Compile ES2015 default and rest parameters to ES5
We found that @babel/plugin-transform-parameters 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.
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