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lodash debounce and throttle source code
const nativeMax = Math.max;
const nativeMin = Math.min;
function debounce(func, wait, options) {
let 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 = Number(wait) || 0;
if (typeof options === 'object') {
leading = !!options.leading;
maxing = 'maxWait' in options;
maxWait = maxing
? nativeMax(Number(options.maxWait) || 0, wait)
: maxWait;
trailing = 'trailing' in options
? !!options.trailing
: trailing;
}
function invokeFunc(time) {
let 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) {
let timeSinceLastCall = time - lastCallTime,
timeSinceLastInvoke = time - lastInvokeTime,
result = wait - timeSinceLastCall;
console.log('remainingWait');
return maxing
? nativeMin(result, maxWait - timeSinceLastInvoke)
: result;
}
function shouldInvoke(time) {
let 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() {
const time = Date.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(Date.now());
}
function debounced() {
let time = Date.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;
}
function throttle(func, wait, options) {
let leading = true,
trailing = true;
if (typeof func !== 'function') {
throw new TypeError(FUNC_ERROR_TEXT);
}
if (typeof options === 'object') {
leading = 'leading' in options
? !!options.leading
: leading;
trailing = 'trailing' in options
? !!options.trailing
: trailing;
}
return debounce(func, wait, {
leading,
maxWait: wait,
trailing,
});
}
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