I'm just starting out with AJAX and I'm trying to get a variable to be set inside a for loop. Then I want to call that variable later and use it's value.
Of course this would be synchronous, requiring the scripts to stop executing in order to run the loop before returning the new value of the function.
I'm hoping someone knows a better way to get the value from the for loop AFTER the for loop has run and use it in my code directly after that.
I would prefer not to use the setTimeout() hack to bypass this issue (it is a hack after all).
var getCount = function getCount(res) {
count = { active: 0, closed: 0 }; //Variable defined here
for(i=0; i<=res.length; i++) {
if(res[i].status == 'active') {
count.active ++;
} else { count.closed ++; }
}
return count; //And returned here
};
getCount(result);
console.log(count); //Here's where I need the result of the for loop
//Currently this outputs the count object with both properties set to 0;
I am not sure what AJAX has to do with your issue.
You are not assigning the result of the getCount function to the count variable (Unless you intended the count variable to be global, but in that case you need to define it before the getCount function definition).
Change this line:
getCount(result);
to this:
var count = getCount(result);
And you should be alright. :)
I would also suggest, when declaring variables, always declare them with var. In your case:
var count = { active: 0, closed: 0};
I don't know why you mention AJAX since there is nothing async about your code.
From what I see in your sample I don't see what all the difficulty is about.
Just use it as any other function.
function getCount(res) {
var count = { active: 0, closed: 0 }; //Variable defined here
for(i=0; i<=res.length; i++) {
if(res[i].status == 'active') {
count.active ++;
} else { count.closed ++; }
}
return count; //And returned here
};
console.log(getCount(result)); //Here's where I need the result of the for loop
First off, you had an extra = sign that was over-extending your for loop. I don't know if this answers your asynchronous issue, but here is how I would do it:
// sample object
var result = [
{status:"active"},
{status:"not-active"},
{status:"active"}
];
// kick off the function to get the count object back
var counts = getCount(result);
console.log(counts);
function getCount(res) {
var count = { active: 0, closed: 0 }; //Variable defined here, make sure you have var to keep it from going global scope
for(i=0; i<res.length; i++) { //here you had a wrong "="
if(res[i].status === 'active') {
count.active ++;
} else { count.closed ++; }
}
return count; //And returned here
}
Example here.
Related
I am new to javascript, my background is python and ruby and I am having issues dealing with javascript anonymous functions, my problem is the following:
I have an element in the page which has an attribute value (true/false), I need to keep performing an action until this attribute changes value.
the code that I tried out is below, as you could guess, the break won't quit the loop if result.value == true... Any idea if I am in the right direction?
var counter = 0;
while (counter < 5) {
this
.click('#someelementid')
counter++;
this
.getAttribute('#someelementid', 'disabled', function(result) {
if (result.value == 'true') {
this.break;
}
}.bind(this));
this.api.pause(1000);
};
My assumption is that by binding this, I have access to the while block? Please correct me if I am wrong.
Have you tried changing your code to something like below ?
var counter = 0;
var arr = [1, 2, 3, 4, 5];
while (counter < 5) {
arr.forEach(
(element) => {
if (counter < 5) { // if you don't have this it will print all 5, else it prints only 3
console.log('Element value:', element);
}
if (element == 3) {
counter = 5;
}
}
);
}
What happens is this:
When you enter the while loop it will enter the forEach loop and start iterating, when it reaches element == 3 it will set counter to 5, but it still has to finish the current forEach loop, once it does it wont perform another while loop therefore exiting it.
So changing your code to:
var counter = 0;
while (counter < 5) {
this
.click('#someelementid')
counter++;
this
.getAttribute('#someelementid', 'disabled', function(result) {
if (result.value == 'true') {
counter = 5; // This should do the trick (without 'this')
}
}.bind(this));
this.api.pause(1000);
};
The break inside a function would not break the loop outside the function.
Through getAttribute() get the result inline instead of having a callback. then you can break the function.
Or
Have a global variable. breakLoop = false; set it to true; inside the callback function. And put a check on this variable in the while loop. while(!breakLoop ..)
Another approach.
Don't have a loop altogether.
var counter = 0;
function doSomething(){
this.click('#someelementid');
counter++;
this.getAttribute('#someelementid', 'disabled', function(result) {
if(result.value != 'true' && counter<5){
this.api.pause(1000);
doSomething();
}
}.bind(this);
};
I am new to coding and I want to built a Text Adeventure Game with HTML , CSS and Javascript. I want to show many peaces of text from an array with a certain time between each text. I tried different methods to avoid an infinite loop because of setTimeout, but I didn't figure out how to apply it on my code.
Here's my code, that causes the crash:
var iCounterText = 0;
var verzog = function() {
document.getElementById('toggleText').insertAdjacentHTML('beforeBegin', '<br>--------------<br>');
document.getElementById('toggleText').insertAdjacentHTML('beforeBegin', part1[iCounterText]);
iCounterText = iCounterText + 1;
playaudio();
}
function forwardingLinks() {
while (iCounterText < part1.length - 1) {
setTimeout(verzog, 500); // Here is the problem //
}
document.getElementById('buttonLinks').innerHTML = part1[part1.length - 1];
}
The following code works fine, but then there is no timeout between the text:
function forwardingLinks() {
while (iCounterText < part1.length - 1) {
verzog();
}
document.getElementById('buttonLinks').innerHTML = part1[part1.length - 1];
}
Edit:
This is my new code with "setInterval". Problem: Value is added by 1, but the function is not using the part2 Array. Instead it is using part1 Array again, although the partvalue already contains part2 array.
var part1 = [ //Texte und Antworten
'Hallo?',
'Test?',
'What',
'hello',
'--------------',
'Was?'
];
var part2 = [ //Texte und Antworten
'part2 goes on....',
'bla bla',
'blablabla'
];
var iCounterText = 0;
var value = 1;
var partvalue = eval("part" + value);
function forwardingLinks() {
var verzog = setInterval(function(){
if(iCounterText < partvalue.length-2){
++iCounterText;
toggleText.insertAdjacentHTML('beforeBegin', '<br>--------------<br>');
toggleText.insertAdjacentHTML('beforeBegin', partvalue[iCounterText]);
playaudio();
}else{
buttonLinks.innerHTML = partvalue[partvalue.length-1];
++value;
iCounterText=0;
clearInterval(verzog);
}
},500);
}
You are misunderstanding the flow of your while loop. JavaScript runs in a single-threaded environment. That means that your calls to the verzog function won't run until the forwardingLinks function completes, but your forwardingLinks function won't ever complete because you have a while loop that is dependent on a counter that is never increased, because verzog hasn't run yet.
Change your while loop, so that the iCounterText variable gets incremented from within the loop, so the loop can end and then the calls to verzog that have stacked up in the event queue can start to run.
Additionally, since you are using a numeric counter, a regular for loop would be better than an while loop because the loop's step value (++iCounterText) is required:
for(var iCounterText = 0; iCounterText < part1.length; ++iCounterText) {
setTimeout(verzog, 500);
}
As an aside from your main problem, it is very inefficient to repeatedly scan the DOM for the same element over and over, as you are doing in your verzog function. Instead, just get the DOM reference once and store it in a variable that can be reused:
// Declare a variable in a scope that is accessible throughout your code
var toggleText = null, buttonLinks = null;
// Set up a callback that runs after the DOM is ready
window.addEventListener("DOMContentLoaded", function(){
// Scan the DOM for the element(s) you'll be needing
toggleText = document.getElementById('toggleText');
buttonLinks = document.getElementById('buttonLinks');
});
function verzog() {
// Now, you can just refer to the DOM element you've already found:
toggleText .insertAdjacentHTML('beforeBegin', '<br>--------------<br>');
toggleText .insertAdjacentHTML('beforeBegin', part1[iCounterText]);
playaudio();
}
function forwardingLinks() {
for(var iCounterText = 0; iCounterText < part1.length; ++iCounterText) {
setTimeout(verzog, 500);
}
// Now, you can just refer to the DOM element you've already found:
buttonLinks.innerHTML = part1[part1.length - 1];
}
Background
I have a plain JS array, initially empty. I later populate it with values. The values sent to it are numbers that are Knockout observables. Later, I want to compare those values to values in another, knockout observable array. My problem is that whenever I pass the index of the current item in my array loop, and pass that index value (a number!), the array returns a function. To get an idea, look at the JS that follows.
Note that my project and actual script is viewable on JSBin. Further, to view the problem in the console, you have to add assignments, then press 'sort'.
JSBin: http://jsbin.com/fehoq/177/edit]1
JS
//example script that follows actual script
var _this = this;
//initialize my array
this. lowest = [];
// I want to compare values in lowest to values in this array
this.scores = ko.observableArray();
// method that does comparison
this.myMethod = function(){
// initialize my helper, k
var k;
...
// loop through one array
ko.utils.arrayForEach(_this.scores(), function (score) {
// make sure my value is a number...
if (!isNaN(parseFloat(score()))) {
// this is important, I need to current index for comparison
k = _this.scores.indexOf(score);
console.log(k);
// this is where things break - it prints a function, not a value!
console.log(_this.lowest[k]);
// useless check, the value is a function, so they're always different
if (score()!=_this.lowest[k]){
// do stuff
}
}
}
}
Update
Putting the method I'm using, maybe someone will notice something I missed given that my syntax is correct(?).
this.mean = (function(scores,i) {
var m = 0;
var count = 0;
var k;
ko.utils.arrayForEach(_this.scores(), function(score) {
console.log([typeof score(), score()]);
if (!isNaN(parseFloat(score()))) {
console.log(i);
console.log(_this.lowest[i]);
if (score() != _this.lowest[i]) {
m += parseFloat(score());
count += 1;
}
}
});
if (count) {
m = m / count;
return m.toFixed(2);
} else {
return 'N/A';
}
});
}
Update 2
Just in case someone else wanders over here since my problem isn't solve still. The following code is how I set the value of lowest:
this.dropLowestScores = function() {
ko.utils.arrayForEach(_this.students(), function(student){
var comparator = function(a,b){
if(a()<b()){
return 1;
} else if(a() > b()){
return -1;
} else {
return 0;
}
};
var tmp = student.scores().slice(0);
tmp.sort(comparator);
student.lowest = ko.observableArray(tmp.splice((tmp.length-2),tmp.length-1));
});
};
Outstanding Questions, 5/9/2014
Jeremy's script runs but without the desired effects. For example, console.log(_this.lowest[k]) prints undefined, just as mine does. Further, the matched scores aren't skipped, which they should be.
Jeremy's script specifies lowest as a ko.observable. My script also now has lowest as a ko.observable, but why shouldn't a plain JS array work for this? I only need lowest to update when the button it's bound to is clicked, and those bindings are already taken care of.
That is how observables work in Knockout.
When you create one, you are creating a function.
var myObservable1 = ko.observable(); // Create it.
var myObservable2 = ko.observable("Hola!"); // Create it with a value.
console.log(typeof myObservable2); // It is indeed a function
console.log(typeof myObservable2()); // That returns a string
console.log(myObservable2()); // And get the value.
EDIT BASED ON QUESTION IN COMMENTS
var koTest = ko.observableArray();
koTest.push("Line0");
koTest.push("Line1");
koTest.push("Line2");
koTest.push("Line3");
koTest.push("Line4");
var jsTest = [];
jsTest.push("Line0");
jsTest.push("Line1");
jsTest.push("Line2");
jsTest.push("Line3");
jsTest.push("Line4");
alert(koTest()[2]);
alert(jsTest[2]);
alert(koTest()[2] === jsTest[2]);
Test Code
I went ahead and make a runnable test of your code and everything was working just fine for me. I had to make some assumptions about the contents of _this -- in particular the declaration of lowest, which I made an observableArray based on how you were accessing it.
Anyways, this code runs:
var _this = {
scores: ko.observableArray(),
lowest: ko.observableArray()
};
var mean = (function(scores) {
var m = 0;
var count = 0;
var k;
ko.utils.arrayForEach(_this.scores(), function(score) {
console.log([typeof score(), score()]);
if (!isNaN(parseFloat(score()))) {
k = _this.scores.indexOf(score);
console.log(k);
console.log(_this.lowest[k]);
if (score() != _this.lowest[k]) {
m += parseFloat(score());
count += 1;
}
}
});
if (count) {
m = m / count;
return m.toFixed(2);
} else {
return 'N/A';
}
});
for (var i = 0; i < 10; i++) {
_this.scores.push(ko.observable(i));
}
var m = mean();
alert(m);
$('#ID').on('click', function() {
if(!CommonUtil.compareDateById('startDt','endDt',false, false, true)) {
return false;
}
var cnt = 0;
if(!CommonUtil.isNullOrEmptyById('startDt')) { cnt++; }
if(cnt == 0) {
CommonUtil.setFocusById('srchWord','<spring:message code="confirm.input" arguments="XXXX"/>');
return false;
So if I click on #ID, following logic occurs.
And my question is what does
var cnt = 0;
if(!CommonUtil.isNullOrEmptyById('startDt')) {
cnt++;
}
mean?
The function of isNullOrEmptyById is following:
isNullOrEmptyById: function(id) {
var value = this.getTrimValueById(id);
return this.isNullOrEmpty(value);
},
But what does
cnt++;
do in here??
This is just an if conditional block:
if(!CommonUtil.isNullOrEmptyById('startDt')) {
cnt++;
}
So if CommonUtil.isNullOrEmptyById('startDt') resolves to false, then the condition resolves to true and the code in the block is executed:
cnt++;
The ++ operator increments the value. So whatever numeric value is in cnt will be incremented by 1.
In the overall context of the code, it seems to be treating cnt as more of a boolean than an integer, though. Unless there's more code outside of this example, this can be simplified by using this condition for the last conditional block instead of using cnt and then checking its value.
It is actually unnecessary. Since the cnt is only incremented once it's value is either 0 or 1. Instead you could just get rid of all that and use isNullOrEmptyById function.
if(!CommonUtil.isNullOrEmptyById('startDt')){
CommonUtil.setFocusById('srchWord','<spring:message code="confirm.input" arguments="XXXX"/>');
return false;
}
Here what I'm trying to do.
I'm having an array like the following
var my_array = ['1', '2', '3' ... ,'1000000000000000'];
What I want to do is create a bunch of HTML elements for every element of that array, and since the array can contain a huge number of elements I attempted to do the following so the browser won't freeze.
for(var i in my_array)
{
if(my_array.hasOwnProperty(i))
{
setTimeout(function(){
do_something_with_data(my_array[i]);
});
}
}
What happens though is that the my_array[i] within the setTimeout doesn't have the value it should.
To be more accurate, when I try to console.log(my_array[i]) what I get is something like this:
"getUnique" function (){
var u = {}, a = [];
for(var i = 0, l = this.length; i < l; ++i){
if(u.hasOwnProperty(this[i])) {
continue;
}
a.push(this[i]);
u[this[i]] = 1;
}
return a;
}
getUnique is a function I've added to the Array prototype just like this:
Array.prototype.getUnique = function(){
var u = {}, a = [];
for(var i = 0, l = this.length; i < l; ++i){
if(u.hasOwnProperty(this[i])) {
continue;
}
a.push(this[i]);
u[this[i]] = 1;
}
return a;
};
Can please somebody help me with this issue?
the setTimeout is executed after the loop is done, and i is the last key or some garbage value at that point. You can capture the i like so:
for (var i in my_array) {
if (my_array.hasOwnProperty(i)) {
(function(capturedI) {
setTimeout(function() {
do_something_with_data(my_array[capturedI]);
});
})(i);
}
}
You should also not use for..in loops for arrays because it's an order of magnitude slower (especially so with the .hasOwnProperty check) than a for loop and the iteration order is not defined
If you have jQuery or willing to add some extra code for older browsers, you can do:
my_array.forEach( function( item ) {
setTimeout( function() {
do_something_with_data( item );
}, 1000);
});
With jQuery:
$.each( my_array, function( index, item ) {
setTimeout( function() {
do_something_with_data( item );
}, 1000);
});
See docs for [].forEach
The problem is that the functions you're creating have a reference to the i variable, not a copy of its value, and so when they run they see i as it is at that point in time (past the end of the array, presumably). (More: Closures are not complicated)
I'd recommend a completely different approach (below), but first, let's look at how to make your existing approach work.
To do what you were trying to do, with the for loop, you have to have the functions close over something that won't change. The usual way to do that is to use a factory function that creates the timeout functions such that they close over the argument to the factory. Or actually, you can pass in the array element's value rather than the index variable.
for(var i in my_array)
{
if(my_array.hasOwnProperty(i))
{
setTimeout(makeFunction(my_array[i]));
}
}
function makeFunction(entry) {
return function(){
do_something_with_data(entry);
};
}
But, I would probably restructure the code so you're not creating masses and masses of function objects unnecessarily. Instead, use one function, and have it close over an index that it increments:
// Assumes `my_array` exists at this point, and that it
// has at least one entry
var i = 0;
setTimeout(tick, 0);
function tick() {
// Process this entry
if (my_array.hasOwnProperty(i)) {
do_something_with_data(my_array[i]);
}
// Move to next
++i;
// If there are any left, schedule the next tick
if (i < my_array.length) {
setTimeout(tick, 0);
}
}
Its just a guess. Try it like:
for(var i in my_array)
{
if(my_array.hasOwnProperty(i))
setTimeout("do_something_with_data('"+my_array[i]+"')", 500);
}