ts_temp/function/once.js

/**
 * Accepts a function `fn` and returns a function that guards invocation of
 * `fn` such that `fn` can only ever be called once, no matter how many times
 * the returned function is invoked. The first value calculated is returned in
 * subsequent invocations.
 *
 * @param {Function} fn The function to wrap in a call-only-once wrapper.
 * @return {Function} The wrapped function.
 * @example
 *
 *      var addOneOnce = once(x => x + 1);
 *      addOneOnce(10); //=> 11
 *      addOneOnce(addOneOnce(50)); //=> 11
 */
export default ((fn) => {
    let called = false;
    let result;
    return (...args) => {
        if (called) {
            return result;
        }
        result = fn(...args);
        called = true;
        return result;
    };
});