/** * The `computed` utility creates a function that will cache its output until * any of the dependent values are dirty. * * @param {...String} dependentKeys The keys of the dependent values. * @param {function} compute The function which computes the value using the * dependent values. * @return {Function} */ export default function computed(...dependentKeys) { const keys = dependentKeys.slice(0, -1); const compute = dependentKeys.slice(-1)[0]; const dependentValues = {}; let computedValue; return function () { let recompute = false; // Read all of the dependent values. If any of them have changed since last // time, then we'll want to recompute our output. keys.forEach((key) => { const value = typeof this[key] === 'function' ? this[key]() : this[key]; if (dependentValues[key] !== value) { recompute = true; dependentValues[key] = value; } }); if (recompute) { computedValue = compute.apply( this, keys.map((key) => dependentValues[key]) ); } return computedValue; }; }