svelte-textfit/src/utils/whilst.js

Svelte action to fit headlines and paragraphs into any element. Ported from react-textfit

/**
 * Ported from react-textfit@1.1.1 
 * The MIT License (MIT)
 * 
 * Copyright (c) 2015 react-textfit
 * */
const noop = () => {};

/**
 * Repeatedly call fn, while test returns true. Calls callback when stopped, or an error occurs.
 *
 * @param {Function} test Synchronous truth test to perform before each execution of fn.
 * @param {Function} fn A function which is called each time test passes. The function is passed a callback(err), which must be called once it has completed with an optional err argument.
 * @param {Function} callback A callback which is called after the test fails and repeated execution of fn has stopped.
 */

export default function whilst(test, iterator, callback = noop) {
    if (test()) {
        iterator(function next(err, ...args) {
            if (err) {
                callback(err);
            } else if (test.apply(this, args)) {
                iterator(next);
            } else {
                callback(null);
            }
        });
    } else {
        callback(null);
    }
}