Babel Plugin Parameter Decorator


Function parameter decorator transform plugin for babel v7, just like typescript parameter decorator

``javascript
function validate(target, property, descriptor) {
const fn = descriptor.value;

descriptor.value = function (...args) {
const metadata = meta_${property};
target[metadata].forEach(function (metadata) {
if (args[metadata.index] === undefined) {
throw new Error(${metadata.key} is required);
}
});

return fn.apply(this, args);
};

return descriptor;
}

function required(key) {
return function (target, propertyKey, parameterIndex) {
const metadata = meta_${propertyKey};
target[metadata] = [
...(target[metadata] || []),
{
index: parameterIndex,
key
}
]
};
}

class Greeter {
constructor(message) {
this.greeting = message;
}

@validate
greet(@required('name') name) {
return "Hello " + name + ", " + this.greeting;
}
}
`

#### NOTE:

This package depends on @babel/plugin-proposal-decorators.

Installation & Usage

npm install @babel/plugin-proposal-decorators babel-plugin-parameter-decorator -D

And the .babelrc looks like:

`
{
"plugins": [
["@babel/plugin-proposal-decorators", { "legacy": true }],
"babel-plugin-parameter-decorator"
]
}
`

By default, @babel/preset-typescript will remove imports only referenced in Decorators.
Since this is prone to break Decorators, make sure disable it by setting onlyRemoveTypeImports to true:

`
{
...
"presets": [
[
"@babel/preset-typescript",
{ "onlyRemoveTypeImports": true }
]
]
...
}
`

Additional

If you'd like to compile typescript files by babel, the file extensions .ts or .tsx expected, or we will get runtime error!

🎊 Hopefully this plugin would get along with typescript private/public keywords in constructor. For example,

`typescript
@Factory
class Greeter {

private counter: Counter = this.sentinel.counter;

constructor(private greeting: string, @Inject(Sentinel) private sentinel: Sentinel) {
}

@validate
greet(@required('name') name: string) {
return "Hello " + name + ", " + this.greeting;
}

count() {
return this.counter.number;
}
}
`
And your .babelrc looks like:

`
{
"presets": [
"@babel/preset-env",
"@babel/preset-typescript"
],
"plugins": [
["@babel/plugin-proposal-decorators", { "legacy": true }],
["@babel/plugin-proposal-class-properties", { "loose" : true }],
"babel-plugin-parameter-decorator"
]
}
``