@dancrumb/fpish/dist/Lazy.js

FP-friendly classes for Typescript

/**
 * Represents a value that is initialized in a lazy manner, i.e. not until it is needed
 */
export class Lazy {
    builder;
    value;
    constructor(builder) {
        this.builder = builder;
    }
    /**
     * Create a Lazy<T> by providing the function that will be called when the value
     * is first needed
     *
     * @param builder - the initializing function. Since this could be doing anything, it can have
     *                  side effects
     */
    static create(builder) {
        return new Lazy(builder);
    }
    /**
     * Gets the value of the lazy object, initializing it, if necessary
     */
    async getValue() {
        if (typeof this.value === 'undefined') {
            this.value = await this.builder();
        }
        return this.value;
    }
    /**
     * Creates a new `Lazy<S>` value. The initializer takes the value of this `Lazy<T>` and uses it
     * to create a `Lazy<S>`
     *
     * Multiple values can be chained; they won't initialize until the last one is resolved.
     *
     * @param builder - the initializing function. Since this could be doing anything, it can have
     *                  side effects
     */
    chain(builder) {
        return Lazy.create(() => this.getValue().then(builder));
    }
}