_.throttle = function(func, wait, options) {
var timeout; // timeHandle
var context, args, result;
var previous = 0;
if (!options) {
options = {};
}
/* ---------------------------------- */
var later = function() {
previous = options.leading === false ? 0 : _.now();
timeout = null; // timeHandle 開鎖
result = func.apply(context, args);
if (!timeout) {
context = args = null;
}
};
/* ---------------------------------- */
var throttled = function() {
console.log('-----------------------');
var now = _.now();
// previous 要等開鎖後才會更新
if (!previous && options.leading === false) {
previous = now;
}
// 還有多久到
var remaining = wait - (now - previous);
context = this;
args = arguments;
console.log('remaining: ', remaining);
if (remaining <= 0 || remaining > wait) {
// 避免計時器超時未開鎖
// 主要是這個 remaining <= 0
// 若過了 wait.time 鎖尚未打開
// 強制開鎖
console.log('a');
if (timeout) {
// 清除鎖
clearTimeout(timeout);
timeout = null;
}
previous = now;
result = func.apply(context, args);
if (!timeout) {
context = args = null;
}
} else if (!timeout && options.trailing !== false) {
// 開鎖了
console.log('b: ', remaining);
// 設置一個時間，並上鎖
timeout = setTimeout(later, remaining);
}
console.log('c: ', remaining);
return result;
};
/* ---------------------------------- */
throttled.cancel = function() {
console.log('cancal');
clearTimeout(timeout);
previous = 0;
timeout = context = args = null;
};
/* ---------------------------------- */
return throttled;
};
