A suite of helper for writing ES2016 (aka ES7) decorators.
Every helper has the same ‘shape’, you use them to build a decorator by providing the required implementation details.
Every helper is tested against:
- object properties,
- object properties accessors,
- object function property shorthand,
- class initializers,
- class static initializers,
- class accessors,
- class static accessors.
Very important disclaimer: all built decorators must be used with parens,
that is in the form @decorator(...args)
. You can anyway invoke it just after
creation to get a parens-free decorator. My personal advice: choose the parens.
import { valueTransformer } from 'decorators-toolbox';
import valueTransformer from 'decorators-toolbox/value-transformer';
Creates a decorator that modifies the value of the property you attach it to.
const multiplier = valueTransformer(m => n => m * n);
// ┬ ┬ ─┬───
// │ │ └─ result
// │ └─ value
// └─ parameter
const target = {
@multiplier(7) // the parameter
value: 5 // the value
};
console.assert(target.value === 35); // the result, 3 × 5
const trimmer = valueTransformer(() => s => s.trim());
const upperCase = valueTransformer(() => s => s.toUpperCase());
const replacer = valueTransformer((from, to) => s => s.split(from).join(to));
const target = {
@trimmer()
@upperCase()
@replacer(',', '--')
get value() {
return this.storage;
},
set value(v) {
this.storage = v;
}
};
// If you use accessors it works with new values too.
target.value = ' so space, very blanks ';
console.assert(target.value === 'SO SPACE-- VERY BLANKS');
import { ensureAccessors } from 'decorators-toolbox';
import ensureAccessors from 'decorators-toolbox/ensure-accessors';
Wraps a decorator in such a way that the descriptor is guaranteed to be of a computed property.
When it has to convert a normal property to a computed one it uses a Symbol to store the value in the object.
const emitOnChange = ensureAccessors(() => (target, name, descriptor) => {
const originalSet = descriptor.set;
// You don’t have to worry about `value` or `initializer`
return {
...descriptor,
set(value) {
this.emit(`change:${ name }`, { value });
if (originalSet) {
this::originalSet(value);
}
}
};
});
class Person extends EventEmitter {
@emitOnChange()
firstName = "";
}
const author = new Person();
author.firstName = 'Pier Paolo'; // fires 'change:firstName'
This library, Decorators Toolbox, is free software ("Licensed Software"); you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; including but not limited to, the implied warranty of MERCHANTABILITY, NONINFRINGEMENT, or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA