GitHub
Twittermaybe
Create a strictly typed TypeObject that also accepts null and undefined values.
type.maybe(Type)
Given a type, returns a TypeObject that will check values against against that type. Throws if the value is not of the provided type or null or undefined.
import { ObservableObject, type } from "can";
class Person extends ObservableObject {
static props = {
first: type.check(String),
last: type.maybe(String)
};
}
let person = new Person({
first: "Matthew",
last: null
});
console.log(person.first, person.last); // "Matthew" null
Parameters
- Type
{function}:A constructor function that values will be checked against.
Use Case
Using type.maybe you can create types that accept a type, null, or undefined. This is useful in cases where a type is optional but it is more convenient to pass a value even when one doesn't exist.
An example is when binding to a child component (such as a StacheElement). Using bindings means you'll always pass something to that child component, you can't pass nothing. Without a good default value you might want to pass undefined.
import { StacheElement, type } from "can";
class Child extends StacheElement {
static view = `
{{# if(this.name) }}
{{name}}
{{ else }}
No name given!
{{/ if }}
`;
static props = {
name: type.maybe(String)
};
}
customElements.define("child-el", Child);
class Parent extends StacheElement {
static view = `
<child-el name:from="this.name" />
`;
static props = {
name: type.maybe(String)
};
}
customElements.define("parent-el", Parent);
let el = new Parent();
document.body.append(el);