var isObject = require('./isObject'), now = require('./now'), toNumber = require('./toNumber'); /** Error message constants. */ var FUNC_ERROR_TEXT = 'Expected a function'; /* Built-in method references for those with the same name as other `lodash` methods. */ var nativeMax = Math.max, nativeMin = Math.min; /** * Creates a debounced function that delays invoking `func` until after `wait` * milliseconds have elapsed since the last time the debounced function was * invoked. The debounced function comes with a `cancel` method to cancel * delayed `func` invocations and a `flush` method to immediately invoke them. * Provide `options` to indicate whether `func` should be invoked on the * leading and/or trailing edge of the `wait` timeout. The `func` is invoked * with the last arguments provided to the debounced function. Subsequent * calls to the debounced function return the result of the last `func` * invocation. * * **Note:** If `leading` and `trailing` options are `true`, `func` is * invoked on the trailing edge of the timeout only if the debounced function * is invoked more than once during the `wait` timeout. * * If `wait` is `0` and `leading` is `false`, `func` invocation is deferred * until to the next tick, similar to `setTimeout` with a timeout of `0`. * * See [David Corbacho's article](https://css-tricks.com/debouncing-throttling-explained-examples/) * for details over the differences between `_.debounce` and `_.throttle`. * * @static * @memberOf _ * @since 0.1.0 * @category Function * @param {Function} func The function to debounce. * @param {number} [wait=0] The number of milliseconds to delay. * @param {Object} [options={}] The options object. * @param {boolean} [options.leading=false] * Specify invoking on the leading edge of the timeout. * @param {number} [options.maxWait] * The maximum time `func` is allowed to be delayed before it's invoked. * @param {boolean} [options.trailing=true] * Specify invoking on the trailing edge of the timeout. * @returns {Function} Returns the new debounced function. * @example * * // Avoid costly calculations while the window size is in flux. * jQuery(window).on('resize', _.debounce(calculateLayout, 150)); * * // Invoke `sendMail` when clicked, debouncing subsequent calls. * jQuery(element).on('click', _.debounce(sendMail, 300, { * 'leading': true, * 'trailing': false * })); * * // Ensure `batchLog` is invoked once after 1 second of debounced calls. * var debounced = _.debounce(batchLog, 250, { 'maxWait': 1000 }); * var source = new EventSource('/stream'); * jQuery(source).on('message', debounced); * * // Cancel the trailing debounced invocation. * jQuery(window).on('popstate', debounced.cancel); */ function debounce(func, wait, options) { var lastArgs, lastThis, maxWait, result, timerId, lastCallTime, lastInvokeTime = 0, leading = false, maxing = false, trailing = true; if (typeof func != 'function') { throw new TypeError(FUNC_ERROR_TEXT); } wait = toNumber(wait) || 0; if (isObject(options)) { leading = !!options.leading; maxing = 'maxWait' in options; maxWait = maxing ? nativeMax(toNumber(options.maxWait) || 0, wait) : maxWait; trailing = 'trailing' in options ? !!options.trailing : trailing; } function invokeFunc(time) { var args = lastArgs, thisArg = lastThis; lastArgs = lastThis = undefined; lastInvokeTime = time; result = func.apply(thisArg, args); return result; } function leadingEdge(time) { // Reset any `maxWait` timer. lastInvokeTime = time; // Start the timer for the trailing edge. timerId = setTimeout(timerExpired, wait); // Invoke the leading edge. return leading ? invokeFunc(time) : result; } function remainingWait(time) { var timeSinceLastCall = time - lastCallTime, timeSinceLastInvoke = time - lastInvokeTime, result = wait - timeSinceLastCall; return maxing ? nativeMin(result, maxWait - timeSinceLastInvoke) : result; } function shouldInvoke(time) { var timeSinceLastCall = time - lastCallTime, timeSinceLastInvoke = time - lastInvokeTime; // Either this is the first call, activity has stopped and we're at the // trailing edge, the system time has gone backwards and we're treating // it as the trailing edge, or we've hit the `maxWait` limit. return (lastCallTime === undefined || (timeSinceLastCall >= wait) || (timeSinceLastCall < 0) || (maxing && timeSinceLastInvoke >= maxWait)); } function timerExpired() { var time = now(); if (shouldInvoke(time)) { return trailingEdge(time); } // Restart the timer. timerId = setTimeout(timerExpired, remainingWait(time)); } function trailingEdge(time) { timerId = undefined; // Only invoke if we have `lastArgs` which means `func` has been // debounced at least once. if (trailing && lastArgs) { return invokeFunc(time); } lastArgs = lastThis = undefined; return result; } function cancel() { if (timerId !== undefined) { clearTimeout(timerId); } lastInvokeTime = 0; lastArgs = lastCallTime = lastThis = timerId = undefined; } function flush() { return timerId === undefined ? result : trailingEdge(now()); } function debounced() { var time = now(), isInvoking = shouldInvoke(time); lastArgs = arguments; lastThis = this; lastCallTime = time; if (isInvoking) { if (timerId === undefined) { return leadingEdge(lastCallTime); } if (maxing) { // Handle invocations in a tight loop. timerId = setTimeout(timerExpired, wait); return invokeFunc(lastCallTime); } } if (timerId === undefined) { timerId = setTimeout(timerExpired, wait); } return result; } debounced.cancel = cancel; debounced.flush = flush; return debounced; } module.exports = debounce;