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Interpretation of throttle debounce source code
2021-08-27 06:40:33 【Little star_ ios】
Concept
throttle( throttle )
A function can only be executed once in a certain time .
debounce( Shake proof )
After the event is triggered , stay n Can only be executed once after seconds , If in n Seconds to trigger the event , The execution time of the function is recalculated .
Source code learning
throttle The implementation of the
function throttle(delay, callback) {
let timeoutID;
let lastExec = 0;
function wrapper() {
const self = this;
const elapsed = Number(new Date()) - lastExec;
const args = arguments;
function exec() {
lastExec = Number(new Date());
callback.apply(self, args);
}
clearTimeout(timeoutID);
if (elapsed > delay) {
exec();
} else {
timeoutID = setTimeout(exec, delay - elapsed);
}
}
return wrapper;
}
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The logic of the whole code is very clear , There are only three steps :
- Calculate the time elapsed since the most recent function execution
elapsed
, And clear the previously set timer . - If the elapsed time is greater than the set time interval
delay
, Then execute the function immediately , And update the execution time of the last function . - If the elapsed time is less than the set time interval
delay
, Then through thesetTimeout
Set a counter , Let the functiondelay - elapsed
Execute after time .
The source code is not difficult to understand , But we need to pay attention to this
Use :
function throttle(delay, callback) {
// ...
function wrapper() {
const self = this;
const args = arguments;
// ...
function exec() {
// ...
callback.apply(self, args);
}
}
}
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In the code above , adopt self
Variables are temporarily saved this
Value , Thus in exec
Function through callback.apply(self, args)
Pass in the right this
value , This is done in Closure Related function calls are very common . Because it's right here this
To deal with , Therefore, the following capabilities can be realized :
function foo() { console.log(this.name); }
const fooWithName = throttle(200, foo);
const obj = {name: 'elvin'};
fooWithName.call(obj, 'elvin');
// => 'elvin'
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debounce Realization
because debounce
n Just postpone the execution time of the function , Do not have throttle
The ability to perform at regular intervals , So it's easier to implement :
function debounce(delay, callback) {
let timeoutID;
function wrapper() {
const self = this;
const args = arguments;
function exec() {
callback.apply(self, args);
}
clearTimeout(timeoutID);
timeoutID = setTimeout(exec, delay);
}
return wrapper;
}
Copy code
Compare the above code with throttle
Compared with the implemented code , It can be found that it is the removal of elapsed
Code after relevant logic , Most of the rest as like as two peas , therefore debounce
Function can be used with throttle
Function implementation (throttle-debounce This is also done in the source code ),throttle
Functions can also use debounce
Function implementation .
Use scenario example
throttle
and debounce
It is applicable to scenarios where users frequently perform the same operation in a short time , for example :
- The user drags the browser window to change the window size , Trigger
resize
event . - The user moves the mouse , Trigger
mousemove
Other events . - The user enters in the input box , Trigger
keydown
|keypress
|keyinput
|keyup
Other events . - The user scrolls the screen , Trigger
scroll
event . - After the user clicks the button , because API The request took too long to see the response immediately , You may keep clicking on the button to trigger
click
event .
To be improved
iOS
Implementation of version .
quote
copyright notice
author[Little star_ ios],Please bring the original link to reprint, thank you.
https://en.qdmana.com/2021/08/20210827064030436S.html
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