This decorator can be applied to
@Injectable
classes to ensure that they are instantiated only once. This is useful for stateful services that belong at the root of the application.
import { Singleton } from '@trademe/ensure';
@Singleton()
@Injectable()
export class MyStatefulService { }
let instance = new MyStatefulService(); // works:
let another = new MyStatefulService(); // throws!
This decorator can be applied to properties on a class to ensure that they conform to rules when they are set. The rules also act as a mechanism for casting values from HTML attributes, which makes for nicer component APIs.
import { Value } from '@trademe/ensure';
export class MyClass {
@Value(isOne) mustBeOne: number;
@Value([isString, isLengthFive]) verySpecificString: string;
}
export function isOne (value: any) {
if (value === 1) {
return value;
}
throw new Error();
}
export function isString (value: string) {
if (typeof value === 'string') {
return value;
}
throw new Error();
}
export function isLengthFive (value: string) {
if (value.length === 5) {
return value;
}
throw new Error();
}
Ensure that a value is not
null
.isNotNull
is special in that it acts when getting the value, not setting it.
import { isNotNull } from '@trademe/ensure';
export class MyClass {
@Value(isNotNull) mustNotBeNull: boolean;
}
let instance = new MyClass();
instance.mustNotBeNull = true; // works
instance.mustNotBeNull = null; // works
console.log(instance.mustNotBeNull): // throws!
Ensure that a value is boolean. Also casts from
'true'
or''
totrue
and'false'
tofalse
.
import { isBool } from '@trademe/ensure';
export class MyClass {
@Value(isBool) mustBeBoolean: boolean;
}
let instance = new MyClass();
instance.mustBeBoolean = true; // works
instance.mustBeBoolean = 'hello'; // throws!
instance.mustBeBoolean = 'false'; // works
console.log(instance.mustBeBoolean) // false
isBool
is particularly useful for simplifying component APIs when combined with@Input
.
import { isBool } from '@trademe/ensure';
@Component({ ... })
export class MyComponent {
@Input() @Value(isBool) mustBeBoolean: boolean;
}
<my-component
mustBeBoolean><!-- No more pesky ="true"! -->
</my-component>
Ensure that a value is a valid enum value.
import { isEnum } from '@trademe/ensure';
export enum MyEnum {
foo,
bar
}
export class MyClass {
@Value(isEnum<typeof MyEnum>(MyEnum)) mustBeEnum: MyEnum;
}
let instance = new MyClass();
instance.mustBeEnum = 'foo'; // works
console.log(instance.mustBeEnum); // 0
instance.mustBeEnum = 'bar'; // works!
console.log(instance.mustBeEnum); // 1
instance.mustBeEnum = 'baz'; // throws!
Ensure that a value is a valid number.
import { isNumber } from '@trademe/ensure';
export class MyClass {
@Value(isNumber) mustBeNumber: number;
}
let instance = new MyClass();
instance.mustBeNumber = 5; // works
console.log(instance.mustBeNumber); // 5
instance.mustBeNumber = '1.33'; // works!
console.log(instance.mustBeNumber); // 1.33
instance.mustBeNumber = 'baz'; // throws!