2a09d1a4
 liuqimichale
添加宜春 天水 宣化
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import requestAnimationFrame from '../shims/requestAnimationFrame.js';
// Defines minimum timeout before adding a trailing call.
const trailingTimeout = 2;
/**
* Creates a wrapper function which ensures that provided callback will be
* invoked only once during the specified delay period.
*
* @param {Function} callback - Function to be invoked after the delay period.
* @param {number} delay - Delay after which to invoke callback.
* @returns {Function}
*/
export default function (callback, delay) {
let leadingCall = false,
trailingCall = false,
lastCallTime = 0;
/**
* Invokes the original callback function and schedules new invocation if
* the "proxy" was called during current request.
*
* @returns {void}
*/
function resolvePending() {
if (leadingCall) {
leadingCall = false;
callback();
}
if (trailingCall) {
proxy();
}
}
/**
* Callback invoked after the specified delay. It will further postpone
* invocation of the original function delegating it to the
* requestAnimationFrame.
*
* @returns {void}
*/
function timeoutCallback() {
requestAnimationFrame(resolvePending);
}
/**
* Schedules invocation of the original function.
*
* @returns {void}
*/
function proxy() {
const timeStamp = Date.now();
if (leadingCall) {
// Reject immediately following calls.
if (timeStamp - lastCallTime < trailingTimeout) {
return;
}
// Schedule new call to be in invoked when the pending one is resolved.
// This is important for "transitions" which never actually start
// immediately so there is a chance that we might miss one if change
// happens amids the pending invocation.
trailingCall = true;
} else {
leadingCall = true;
trailingCall = false;
setTimeout(timeoutCallback, delay);
}
lastCallTime = timeStamp;
}
return proxy;
}
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