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How to implement the lodash _.throttle in vanilla javascript? [duplicate]

I am looking for a simple throttle in JavaScript. I know libraries like lodash and underscore have it, but only for one function it will be overkill to include any of those libraries.
I was also checking if jQuery has a similar function - could not find.
I have found one working throttle, and here is the code:
function throttle(fn, threshhold, scope) {
threshhold || (threshhold = 250);
var last,
deferTimer;
return function () {
var context = scope || this;
var now = +new Date,
args = arguments;
if (last && now < last + threshhold) {
// hold on to it
clearTimeout(deferTimer);
deferTimer = setTimeout(function () {
last = now;
fn.apply(context, args);
}, threshhold);
} else {
last = now;
fn.apply(context, args);
}
};
}
The problem with this is: it fires the function once more after the throttle time is complete. So let's assume I made a throttle that fires every 10 seconds on keypress - if I do keypress 2 times, it will still fire the second keypress when 10 seconds are completed. I do not want this behavior.

I would use the underscore.js or lodash source code to find a well tested version of this function.
Here is the slightly modified version of the underscore code to remove all references to underscore.js itself:
// Returns a function, that, when invoked, will only be triggered at most once
// during a given window of time. Normally, the throttled function will run
// as much as it can, without ever going more than once per `wait` duration;
// but if you'd like to disable the execution on the leading edge, pass
// `{leading: false}`. To disable execution on the trailing edge, ditto.
function throttle(func, wait, options) {
var context, args, result;
var timeout = null;
var previous = 0;
if (!options) options = {};
var later = function() {
previous = options.leading === false ? 0 : Date.now();
timeout = null;
result = func.apply(context, args);
if (!timeout) context = args = null;
};
return function() {
var now = Date.now();
if (!previous && options.leading === false) previous = now;
var remaining = wait - (now - previous);
context = this;
args = arguments;
if (remaining <= 0 || remaining > wait) {
if (timeout) {
clearTimeout(timeout);
timeout = null;
}
previous = now;
result = func.apply(context, args);
if (!timeout) context = args = null;
} else if (!timeout && options.trailing !== false) {
timeout = setTimeout(later, remaining);
}
return result;
};
};
Please note that this code can be simplified if you don't need all the options that underscore support.
Please find below a very simple and non-configurable version of this function:
function throttle (callback, limit) {
var waiting = false; // Initially, we're not waiting
return function () { // We return a throttled function
if (!waiting) { // If we're not waiting
callback.apply(this, arguments); // Execute users function
waiting = true; // Prevent future invocations
setTimeout(function () { // After a period of time
waiting = false; // And allow future invocations
}, limit);
}
}
}
Edit 1: Removed another reference to underscore, thx to #Zettam 's comment
Edit 2: Added suggestion about lodash and possible code simplification, thx to #lolzery #wowzery 's comment
Edit 3: Due to popular requests, I added a very simple, non-configurable version of the function, adapted from #vsync 's comment

What about this?
function throttle(func, timeFrame) {
var lastTime = 0;
return function () {
var now = Date.now();
if (now - lastTime >= timeFrame) {
func();
lastTime = now;
}
};
}
Simple.
You may be interested in having a look at the source.

callback: takes the function that should be called
limit: number of times that function should be called within the time limit
time: time span to reset the limit count
functionality and usage: Suppose you have an API that allows user to call it 10 times in 1 minute
function throttling(callback, limit, time) {
/// monitor the count
var calledCount = 0;
/// refresh the `calledCount` varialbe after the `time` has been passed
setInterval(function(){ calledCount = 0 }, time);
/// creating a closure that will be called
return function(){
/// checking the limit (if limit is exceeded then do not call the passed function
if (limit > calledCount) {
/// increase the count
calledCount++;
callback(); /// call the function
}
else console.log('not calling because the limit has exceeded');
};
}
////////////////////////////////////////////////////////////
// how to use
/// creating a function to pass in the throttling function
function cb(){
console.log("called");
}
/// calling the closure function in every 100 milliseconds
setInterval(throttling(cb, 3, 1000), 100);

Adding to the discussion here (and for more recent visitors), if the reason for not using the almost de facto throttle from lodash is to have a smaller sized package or bundle, then it's possible to include only throttle in your bundle instead of the entire lodash library. For example in ES6, it would be something like:
import throttle from 'lodash/throttle';
Also, there is a throttle only package from lodash called lodash.throttle which can be used with a simple import in ES6 or require in ES5.

I've just needed a throttle/debounce function for window resize event, and being curious, I also wanted to know what these are and how they work.
I've read multiple blog posts and QAs on SO, but they all seem to overcomplicate this, suggest libraries, or just provide descriptions and not simple plain JS implementations.
I won't provide a description since it's plentiful. So here's my implementation:
function throttle(callback, delay) {
var timeoutHandler = null;
return function () {
if (timeoutHandler == null) {
timeoutHandler = setTimeout(function () {
callback();
timeoutHandler = null;
}, delay);
}
}
}
function debounce(callback, delay) {
var timeoutHandler = null;
return function () {
clearTimeout(timeoutHandler);
timeoutHandler = setTimeout(function () {
callback();
}, delay);
}
}
These might need tweaks (e.g., initially the callback isn't called immediately).
See the difference in action (try resizing the window):
function throttle(callback, delay) {
var timeoutHandler = null;
return function () {
if (timeoutHandler == null) {
timeoutHandler = setTimeout(function () {
callback();
timeoutHandler = null;
}, delay);
}
}
}
function debounce(callback, delay) {
var timeoutHandler = null;
return function () {
clearTimeout(timeoutHandler);
timeoutHandler = setTimeout(function () {
callback();
}, delay);
}
}
var cellDefault = document.querySelector("#cellDefault div");
var cellThrottle = document.querySelector("#cellThrottle div");
var cellDebounce = document.querySelector("#cellDebounce div");
window.addEventListener("resize", function () {
var span = document.createElement("span");
span.innerText = window.innerWidth;
cellDefault.appendChild(span);
cellDefault.scrollTop = cellDefault.scrollHeight;
});
window.addEventListener("resize", throttle(function () {
var span = document.createElement("span");
span.innerText = window.innerWidth;
cellThrottle.appendChild(span);
cellThrottle.scrollTop = cellThrottle.scrollHeight;
}, 500));
window.addEventListener("resize", debounce(function () {
var span = document.createElement("span");
span.innerText = window.innerWidth;
cellDebounce.appendChild(span);
cellDebounce.scrollTop = cellDebounce.scrollHeight;
}, 500));
table {
border-collapse: collapse;
margin: 10px;
}
table td {
border: 1px solid silver;
padding: 5px;
}
table tr:last-child td div {
width: 60px;
height: 200px;
overflow: auto;
}
table tr:last-child td span {
display: block;
}
<table>
<tr>
<td>default</td>
<td>throttle</td>
<td>debounce</td>
</tr>
<tr>
<td id="cellDefault">
<div></div>
</td>
<td id="cellThrottle">
<div></div>
</td>
<td id="cellDebounce">
<div></div>
</td>
</tr>
</table>
JSFiddle

Here's how I implemented throttle function in ES6 in 9LOC, hope it helps
function throttle(func, delay) {
let timeout = null
return function(...args) {
if (!timeout) {
timeout = setTimeout(() => {
func.call(this, ...args)
timeout = null
}, delay)
}
}
}
Click on this link to see how it works.

I've seen a lot of answers here that are way too complex for "a simple throttle in js".
Almost all of the simpler answers just ignore calls made "in throttle" instead of delaying execution to the next interval.
Here's a simple implementation that also handles calls "in throttle":
const throttle = (func, limit) => {
let lastFunc;
let lastRan = Date.now() - (limit + 1); //enforces a negative value on first run
return function(...args) {
const context = this;
clearTimeout(lastFunc);
lastFunc = setTimeout(() => {
func.apply(context, args);
lastRan = Date.now();
}, limit - (Date.now() - lastRan)); //negative values execute immediately
}
}
This is almost the exact same implementation for a simple debounce. It just adds a calculation for the timeout delay which requires tracking when the function was last ran. See below:
const debounce = (func, limit) => {
let lastFunc;
return function(...args) {
const context = this;
clearTimeout(lastFunc);
lastFunc = setTimeout(() => {
func.apply(context, args)
}, limit); //no calc here, just use limit
}
}

Simple solution in ES6. Codepen Demo
const handleOnClick = () => {
console.log("hello")
}
const throttle = (func, delay) => {
let timeout = null;
return function (...args) {
if (timeout === null) {
func.apply(this, args);
timeout = setTimeout(() => {
timeout = null;
}, delay)
}
}
}
document.querySelector("#button").addEventListener("click", throttle(handleOnClick, 500))
<button type="button" id="button">Click me</button>

Here's my own version of Vikas post:
throttle: function (callback, limit, time) {
var calledCount = 0;
var timeout = null;
return function () {
if (limit > calledCount) {
calledCount++;
callback();
}
if (!timeout) {
timeout = setTimeout(function () {
calledCount = 0
timeout = null;
}, time);
}
};
}
I find that using setInterval is not a good idea.

With leading and trailing invocations:
const throttle = (fn, ms) => {
let locked = false
return function () {
if (!locked) {
locked = true
fn.apply(this, arguments)
setTimeout(() => {
fn.apply(this, arguments)
locked = false
}, ms)
}
}
}
Test case:
function log({ gender, address }) {
console.log({
name: this.name,
gender,
address,
})
}
const jack = {
name: 'Jack',
log: throttle(log, 3000),
}
Array.from({ length: 5 }, () => jack.log({ gender: 'Male', address: 'LA' }))

I made a npm package with some throttling functions:
npm install function-throttler
throttleAndQueue
Returns a version of your function that can be called at most every W milliseconds, where W is wait. Calls to your func that happen more often than W get queued up to be called every W ms
throttledUpdate
Returns a version of your function that can be called at most every W milliseconds, where W is wait. for calls that happen more often than W the last call will be the one called (last takes precedence)
throttle
limits your function to be called at most every W milliseconds, where W is wait. Calls over W get dropped

There is a library suited for this purpose, it's Backburner.js from Ember.
https://github.com/BackburnerJS/
You'd use it so.
var backburner = new Backburner(["task"]); //You need a name for your tasks
function saySomething(words) {
backburner.throttle("task", console.log.bind(console, words)
}, 1000);
}
function mainTask() {
"This will be said with a throttle of 1 second per word!".split(' ').map(saySomething);
}
backburner.run(mainTask)

This throttle function is build on ES6. Callback functions takes arguments (args), and still it works wrapped with throttle function. Be free to customize delay time according to your app needs. 1 time per 100ms is used for development mode, event "oninput" is just an example for frequent case of its use:
const callback = (...args) => {
console.count('callback throttled with arguments:', args);
};
throttle = (callback, limit) => {
let timeoutHandler = 'null'
return (...args) => {
if (timeoutHandler === 'null') {
timeoutHandler = setTimeout(() => {
callback(...args)
timeoutHandler = 'null'
}, limit)
}
}
}
window.addEventListener('oninput', throttle(callback, 100));
P.S. As #Anshul explained: throttling enforces a maximum number of times a function can be called over time. As in "execute this function at most once every 100 milliseconds."

In below example, try clicking the button multiple times, but the myFunc function would be executed only once in 3 sec.
The function throttle is passed with the function to be executed and the delay.It returns a closure, which is stored in obj.throttleFunc.
Now since obj.throttleFunc stores a closure, the value of isRunning is maintained inside it.
function throttle(func, delay) {
let isRunning;
return function(...args) {
let context = this; // store the context of the object that owns this function
if(!isRunning) {
isRunning = true;
func.apply(context,args) // execute the function with the context of the object that owns it
setTimeout(function() {
isRunning = false;
}, delay);
}
}
}
function myFunc(param) {
console.log(`Called ${this.name} at ${param}th second`);
}
let obj = {
name: "THROTTLED FUNCTION ",
throttleFunc: throttle(myFunc, 3000)
}
function handleClick() {
obj.throttleFunc(new Date().getSeconds());
}
button {
width: 100px;
height: 50px;
font-size: 20px;
}
<button onclick="handleClick()">Click me</button>
If we don't want the context or arguments to be passed, then a simpler
version of this would be as following:
function throttle(func, delay) {
let isRunning;
return function() {
if(!isRunning) {
isRunning = true;
func()
setTimeout(function() {
isRunning = false;
}, delay);
}
}
}
function myFunc() {
console.log('Called');
}
let throttleFunc = throttle(myFunc, 3000);
function handleClick() {
throttleFunc();
}
button {
width: 100px;
height: 50px;
font-size: 20px;
}
<button onclick="handleClick()">Click me</button>

I also want to suggest a simple solution for when there is only 1 function you know you will call (for example: Search)
here is what i did in my project
let throttle;
function search() {
if (throttle) {
clearTimeout(throttle);
}
throttle = setTimeout(() => {
sendSearchReq(str)
}, 500);
}
Search is called on input change event

function throttle(targetFunc, delay){
let lastFunc;
let lastTime;
return function(){
const _this = this;
const args = arguments;
if(!lastTime){
targetFunc.apply(_this, args);
lastTime = Date.now();
} else {
clearTimeout(lastFunc);
lastFunc = setTimeout(function(){
targetFunc.apply(_this, args);
lastTime = Date.now();
}, delay - (Date.now() - lastTime));
}
}
}
Try it :
window.addEventListener('resize', throttle(function() {
console.log('resize!!');
}, 200));

CodeSandbox
const { now } = Date;
export default function throttle(func, frameDuration) {
let timeout = null;
let latest;
const epoch = now();
function getDurationToNextFrame() {
const elapsed = now() - epoch;
const durationSinceLastFrame = elapsed % frameDuration;
return frameDuration - durationSinceLastFrame;
}
function throttled(...args) {
latest = () => {
func.apply(this, args);
};
if (!timeout) {
timeout = setTimeout(() => {
latest();
timeout = null;
}, getDurationToNextFrame());
}
}
return throttled;
}

Simple throttle function -
Note- Keep on clicking on the button , You'll see console log at first on click and then only after every 5 seconds until you're keep clicking.
HTML -
<button id='myid'>Click me</button>
Javascript -
const throttle = (fn, delay) => {
let lastTime = 0;
return (...args) => {
const currentTime = new Date().getTime();
if((currentTime - lastTime) < delay) {
return;
};
lastTime = currentTime;
return fn(...args);
}
};
document.getElementById('myid').addEventListener('click', throttle((e) => {
console.log('I am clicked');
}, 5000));

We can also implement using a flag-
var expensive = function(){
console.log("expensive functionnns");
}
window.addEventListener("resize", throttle(expensive, 500))
function throttle(expensiveFun, limit){
let flag = true;
return function(){
let context = this;
let args = arguments;
if(flag){
expensiveFun.apply(context, args);
flag = false;
setTimeout(function(){
flag = true;
}, limit);
}
}
}

Here is a bit modernized and simplified version of #clément-prévost answer
function throttle(func, wait, options = {}) {
let timeout = null;
let previous = 0;
const later = (...args) => {
previous = options.leading === false ? 0 : Date.now();
func(...args);
};
return (...args) => {
const now = Date.now();
if (!previous && options.leading === false) {
previous = now;
}
const remaining = wait - (now - previous);
if (remaining <= 0 || remaining > wait) {
if (timeout) {
clearTimeout(timeout);
timeout = null;
}
previous = now;
func(...args);
} else if (options.trailing !== false) {
clearTimeout(timeout);
timeout = setTimeout(() => later(...args), remaining);
}
};
}
function myFunc(a) {
console.log(`Log: ${a} ${this.val}`);
}
const myFuncThrottled = throttle(myFunc.bind({val: 42}), 1234, {leading: true, trailing: true})
myFuncThrottled(1)
myFuncThrottled(2)
myFuncThrottled(3)

function throttle(CB,ms=300,Id='Identifier for the callback(CB)'){
Id = Id || ""+CB
var N = throttle.N = throttle.N || {}; // Static variable N to store all callbacks ids and their status
if( N[Id] ) return; // already in the queue to run
N[Id] = 1; // add it the queue
setTimeout(()=>{
N[Id] = 0; // remove it from the queue
CB(); // finally call the function
}, ms);
}
for(var i=0;i<100;i++){
throttle(e=>console.log("Hi1"),1e3,'F1');
}
// will only output : Hi1
// this function guarantee the callback to run at least once

Some great solutions here already, but I was looking for a modern version with trailing (and optionally leading) executions, with the last passed arguments provided to each function call:
const throttle = (fn, wait=500, leading=true) => {
let prev, timeout, lastargs;
return (...args) => {
lastargs = args;
if (timeout) return;
timeout = setTimeout(() => {
timeout = null;
prev = Date.now();
// let's do this ... we'll release the stored args as we pass them through
fn.apply(this, lastargs.splice(0, lastargs.length));
// some fancy timing logic to allow leading / sub-offset waiting periods
}, leading ? prev && Math.max(0, wait - Date.now() + prev) || 0 : wait);
};
}
Usage:
x = throttle((...args) => console.log(...args));
let n = 0;
x(++n, 'boom');
x(++n, 'boom');
x(++n, 'boom');

if there will be more than one function defining them one by one would not be maintainable so i would suggest use a helper class to keep values for each
class slowDown {
constructor(cb,timeGap){
this.last = 0
this.run = function(){
let current = Date.now(),
shouldRun = (current - this.last) >= timeGap
if(shouldRun){
cb(current - this.last)
this.last = current
}
}
}
}
// example use
const press = new slowDown(timeElapsed => {
// define function here which you wanted to slow down
console.log("pressed after " + timeElapsed + " ms")
},750)
window.addEventListener("keydown",()=>{
press.run()
})

Below is the simplest throttle I could think of, in 13 LOC. It creates a timeout each time the function is called and cancels the old one. The original function is called with the proper context and arguments, as expected.
function throttle(fn, delay) {
var timeout = null;
return function throttledFn() {
window.clearTimeout(timeout);
var ctx = this;
var args = Array.prototype.slice.call(arguments);
timeout = window.setTimeout(function callThrottledFn() {
fn.apply(ctx, args);
}, delay);
}
}
// try it out!
window.addEventListener('resize', throttle(function() {
console.log('resize!!');
}, 200));

How to execute synchronously using setInterval or setTimeOut?

I have a function as below:
function foo(args1, args2, retry)
{
if (retry <= 0)
return false;
var isDone = callAnotherFunction(args1, args2);
if(!isDone) {
setInterval(function () {
foo(args1, args2, retry-1);
},
2000);
}
else
return true;
}
So I am not sure if the above implementation is correct. But I need to use this function in another function. And use the above function in an if block to decide if the other statement needs to be executed. Below is the usage of the above function.
function useIt(args1, args2)
{
// Other code
let store = function() {
if(!foo(args1, args2, 5)) {
cleanStorage(args1, args2);
return;
}
}
So the problem is in function useIt(), cleanStorage() does not wait for foo() to be executed if I am using setInterval or setTimeOut. So how do I need to implement the function foo() ? Kindly help me.

consider using promises
foo can be rewritten like this (I've replace setInterval with setTimeout):
function foo(args1, args2, retry) {
return new Promise(function (resolve, reject) {
if (retry <= 0)
reject();
var isDone = callAnotherFunction(args1, args2);
if (!isDone) {
setTimeout(function () {
resolve(foo(args1, args2, retry - 1));
}, 2000);
}
else
resolve(true);
})
}
and then use it like this:
function useIt(args1, args2) {
// Other code
let store = function () {
foo(args1, args2, 5).then(function () {
cleanStorage(args1, args2);
});
}
}

You should use Promises to do this
Something like this:
function foo(args1, args2, retry)
{
return new Promise(function(resolve, reject) {
if (retry <= 0)
reject();
var isDone = callAnotherFunction(args1, args2);
if(!isDone) {
setInterval(function () {
retry = retry - 1;
isDone = callAnotherFunction(args1, args2);
if (isDone)
resolve();
},
2000);
}
else
resolve();
}
}
function useIt(args1, args2)
{
// Other code
let store = function() {
foo(args1, args2, 5).then(result => {
cleanStorage(args1, args2);
return;
}
}
}

How to run a function after two async functions complete

Say I have an array of functions that invoke a setTimeout.
[
function(cb){
setTimeout(function(){
cb('one');
}, 200);
},
function(cb){
setTimeout(function(){
cb('two');
}, 100);
}
]
Is there a way to access the time parameter (200, 100) and save the sum of that to a variable?
I want to execute a function only when both of those functions are done

A better approach is to use promises and Promise.all:
var task1 = new Promise(function(resolve,reject) {
setTimeout(function() {
//do something
resolve();
}, 100);
});
var task2 = new Promise(function(resolve,reject) {
setTimeout(function() {
//do something
resolve();
}, 200);
});
Promise.all([task1, task2]).then(function() {
//will be executed when both complete
});

You can mimic it with a closure for the count.
function out(s) {
var node = document.createElement('div');
node.innerHTML = s + '<br>';
document.getElementById('out').appendChild(node);
}
var f = [
function (cb) { setTimeout(function () { cb('one'); }, 100); },
function (cb) { setTimeout(function () { cb('two'); }, 200); }
],
useCounter = function () {
var count = 2;
return function (s) {
count--;
out(s + ' ' + count);
!count && out('done');
}
}();
f[0](useCounter);
f[1](useCounter);
<div id="out"></div>

Execute function queue in javascript

I'm trying to create a function queue with several functions in it.
After the creation i want to execute each function in it's turn.
But these function have delayed instructions inside of them, so i want to wait for each of the functions to complete its execution before the continuing.
My attempts:
var funqueue = [];
funqueue.push( function() {fun1() });
funqueue.push( function() {fun2() });
funqueue.push( function() {fun3() });
executeFunctionQueue(funqueue);
Where the execute function is:
function executeFunctionQueue(funqueue){
var fun1=funqueue.pop;
$.when(fun1()).then(executeFunctionQueue(funqueue));
}
But this does not work.
How should i do it?

Try utilizing .queue() , .promise() ; see also Change easing functions on animations in jQuery queue
function fun1() {
return $.Deferred(function(dfd) {
setTimeout(function() {
dfd.resolve(1)
}, 1500)
}).promise().then(msg)
}
function fun2() {
return $.Deferred(function(dfd) {
setTimeout(function() {
dfd.resolve(2)
}, 1500)
}).promise().then(msg)
}
function fun3() {
return $.Deferred(function(dfd) {
setTimeout(function() {
dfd.resolve(3)
}, 1500)
}).promise().then(msg)
}
var funqueue = [];
funqueue.push(function() {
return fun1()
});
funqueue.push(function() {
return fun2()
});
funqueue.push(function() {
return fun3()
});
function msg(data) {
if (data === "complete") console.log(data)
else $("body").append(data + "<br>")
}
function executeFunctionQueue(funqueue) {
var deferred = funqueue.pop();
return deferred().then(function() {
// set `this` within `$.queue()` , `.then()` to empty object `{}`,
// or other object
return $({}).queue("fun", $.map(funqueue, function(fn) {
return function(next) {
// return `next` function in `"fun"` queue
return fn().then(next)
}
})).dequeue("fun").promise("fun")
.then(function() {
// return "complete" string when `fun` queue empty
return "complete"
})
});
}
executeFunctionQueue(funqueue)
.then(msg);
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js">
</script>
Alternatively , using $.when()
function executeFunctionQueue(funqueue) {
return $.when(!!funqueue[funqueue.length - 1]
? funqueue.pop().call().then(function() {
return executeFunctionQueue(funqueue)})
: "complete")
}
executeFunctionQueue(funqueue)
.then(function(complete) {
console.log(complete)
});
function fun1() {
return $.Deferred(function(dfd) {
setTimeout(function() {
dfd.resolve(1)
}, 1500)
}).promise().then(msg)
}
function fun2() {
return $.Deferred(function(dfd) {
setTimeout(function() {
dfd.resolve(2)
}, 1500)
}).promise().then(msg)
}
function fun3() {
return $.Deferred(function(dfd) {
setTimeout(function() {
dfd.resolve(3)
}, 1500)
}).promise().then(msg)
}
var funqueue = [];
funqueue.push(function() {
return fun1()
});
funqueue.push(function() {
return fun2()
});
funqueue.push(function() {
return fun3()
});
function msg(data) {
if (data === "complete") console.log(data)
else $("body").append(data + "<br>")
}
function executeFunctionQueue(funqueue) {
return $.when(!!funqueue[funqueue.length - 1]
? funqueue.pop().call().then(function() {
return executeFunctionQueue(funqueue)})
: "complete")
}
executeFunctionQueue(funqueue)
.then(msg);
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js">
</script>

If you have functions that return Promises, this can be done very simply with a function like sequence:
// sequence :: [(undefined -> Promise<undefined>)] -> Promise<undefined>
function sequence(fns) {
var fn = fns.shift();
return fn ? fn().then(sequence.bind(null, fns)) : Promise.resolve(undefined);
}
sequence assumes that your asynchronous/Promise-returning functions do not take any inputs and do not produce any outputs (that they are merely being called for side-effects.)
An example usage of the sequence function is:
sequence([f1, f2, f3]);
function f1() {
return new Promise(function (res) {
setTimeout(function () {
console.log('f1');
res();
}, 100);
});
}
function f2() {
return new Promise(function (res) {
setTimeout(function () {
console.log('f2');
res();
}, 1100);
});
}
function f3() {
return new Promise(function (res) {
setTimeout(function () {
console.log('f3');
res();
}, 10);
});
}
This will log out 'f1', 'f2', and 'f3' in order with the varying, specified time delays in between.

Use this
function executeFunctionQueue(funqueue){
if(!funqueue.length){
return
}
var fun1=funqueue.pop();
$.when(fun1()).then(function(){
executeFunctionQueue(funqueue)
});
}
Or even this if queued functions are not asynchronous.
function executeFunctionQueue(funqueue){
var fun=funqueue.pop();
fun()
if(!funqueue.length){
return
}
executeFunctionQueue(funqueue);
}

First create an array of functions as given:
var array_of_functions = [function1, function2, function3, function4];
When you want to execute a given function in the array try this:
array_of_functions[index]('mystring');

use deferred/promise pattern to execute functions on other function complete.
var createQueue = function () {
var d = $.Deferred(),
p = d.promise(),
triggerQueue = function () {
d.resolve();
};
return {
addToQueue: p.then,
triggerQueue: triggerQueue
}
};
var cq = createQueue();
cq.addToQueue(function () {
console.log("hi");
}).then(function () {
console.log("hello");
});
cq.triggerQueue();

In order to make a clean queue, your asynchronous functions will need to somehow signify when they are done, or the next function won't know when to begin. This means you cannot pass in just any old function; they'll need to follow some format. I'd suggest taking a done callback as the first parameter in your function calls. This way, you can support both synchronous and asynchronous functions.
var processQueue = function nextStep(queue) {
var next = queue.shift();
next && next(function() { nextStep(queue); });
}
function fun1(done) {
setTimeout(function() {
console.info('1');
done();
}, 1000);
}
function fun2(done) {
console.info('2');
done();
}
processQueue([fun1, fun2]);
// >> 1 second wait
// >> 1
// >> 2

Excecute JavaScript function after previous one completes

I want to execute several JavaScript functions in a specific order (like below) and not until the previous function has completed. I have tried this so many ways. Any suggestions? Any help is so greatly appreciated, I have been stuck on this for so long. Thanks in advance!
function savedSearch(e){
applySearch1("ColumnA");
applySearch2("ColumnB");
applySearch3("ColumnC");
applySearch4("ColumnD");
applySearch5("ColumnE");
applySearch6("ColumnF");
}

To add in response to the other answer by Mohkhan, you can also use the async library.
https://github.com/caolan/async
That will keep you out of callback hell and make for a much easier to read list of functions.

You should use callbacks in all your applySearch* functions.
Like this.
function savedSearch(e){
applySearch1("ColumnA", function(){
applySearch2("ColumnB", function(){
applySearch3("ColumnC", function(){
applySearch4("ColumnD", function(){
applySearch5("ColumnE",function(){
applySearch6("ColumnF", function(){
// You are done
});
});
});
});
});
});
}

If use jquery, it has deferred objects which helps you deal with async functions.
Here is an example:
// Code goes here
$(document).ready(function() {
function Pipe() {
this.asyncTasks = [];
this.observers = {};
this.on = function(eventName, fn) {
if (!this.observers[eventName]) {
this.observers[eventName] = $.Callbacks;
}
this.observers[eventName].add(fn);
}
this.fire = function(eventName, data) {
if (this.observers[eventName]) {
this.observers[eventName].fire(data);
}
}
this.register = function(asyncFn, context) {
this.asyncTasks.push(new Task(asyncFn, context));
}
this.start = function() {
this.fire('start');
this._next();
}
this._next = function() {
var task = this.asyncTasks.shift();
if (task) {
task.execute().then($.proxy(this._next, this));
} else {
this.fire('end');
}
}
var Task = function(fn, context) {
this.fn = fn;
this.context = context;
this.execute = function() {
if (!this.fn) {
throw new Exception("Failed to execute.");
}
var promise = this.fn.call(context);
this.fn = null;
return promise;
}
}
}
var bookMoview = function() {
var dfd = jQuery.Deferred();
// Resolve after a random interval
setTimeout(function() {
dfd.resolve("The movie is booked");
console.log("The movie is booked");
}, Math.floor(400 + Math.random() * 2000));
// Return the Promise so caller can't change the Deferred
return dfd.promise();
}
var bookTaxi = function() {
var dfd = jQuery.Deferred();
// Resolve after a random interval
setTimeout(function() {
console.log("Taxi is booked");
dfd.resolve("Taxi is booked");
}, Math.floor(400 + Math.random() * 2000));
// Return the Promise so caller can't change the Deferred
return dfd.promise();
}
var pipe = new Pipe();
pipe.register(bookMoview);
pipe.register(bookTaxi);
pipe.start();
});