I'm working on an assignment where a boolean has to switch after a variable is matched to a value in an array. The variable has to be matched with the value in the array using a for loop. However, I'm able to switch the boolean before I introduce the for loop. But after I introduce the for loop, the boolean is stuck to its original value of false.
Can somebody explain why this is happening?
Can I also request, I'm not looking for 'how to do this' but rather an explanation as to why is it happening - so I will appreciate if you do not recommend to me 'another better way' of achieving this - I just want to understand the concept as I'm a beginner.
The code I'm using before the for loop (which changes the boolean correctly) is:
var c = 3;
var w = [];
var m = false;
w.push(3,4);
if (c === w[0]){
m = true;
}
alert (m);
However after I add the for loop counter and also change the if condition from c===w[0] to c===w[i], I only get the 'false' alert using the below code:
var c = 3;
var w = [];
var m = false;
w.push(3,4);
for (i=0; i<2 && c!==w[i]; i++){
if (c === w[i]){
m = true;
}
}
alert (m);
Instead of using for loop, if you only wish that the boolean variable must be switched on satisfying only one condition, you can use some() method. Using this, the loop will not iterate through all the objects and will stop once your condition is satisfied. Example shown below:-
var arr = [3,4,5];
var m = 4;
var bool = false;
array.some(function(item) {
if (m === item){
bool = true;
}
});
alert(bool);
So this will basically give you alert true once you get the matching object from an array.
The condition from for is checked also before first iteration, so the if is not fired. Check out code like this:
var c=3;
var w=[];
w.push(3,4);
var m=false;
for (var i=0;i<2 && c!==w[i];i++){
console.log('In loop')
if (c===w[i]){
m=true;
}
}
Related
I am new in react native , I want to insert new value into every object of array.
I have successfully implemented the logic according to object value. Condition is working right, I have checked by console.log() the statement working right but when I print the my final output array the new value of every object is same, value not assign different in object according to condition.
Here is the code which I am using:-
var newOffers = [];
response.data.forEach((element) => {
for (let i = 0; i < element.frequency; i++) {
var offer = element;
if (offer.used == 0) {
offer.isAvailable = "true";
newOffers.push(offer);
} else {
if (offer.frequency - i <= offer.used) {
console.log("True calling", offer.frequency - i);
offer.isAvailable = "false";
newOffers.push(offer);
} else {
console.log("False calling", offer.frequency - i);
offer.isAvailable = "true";
newOffers.push(offer);
}
}
}
});
console.log("All offers ", newOffers);
I have assign "isAvailable" value "true" or "false" to offer object and all condition working perfectly but when I print the "newOffers" array after complete the loop process the all "isAvailable" values is "false"
What wrong with this code? can someone help me?
In javascript when you use = operator for the objects, it doesn't work like as you expect. You should change your code like this if you are familiar with ES6:
var offer = {...element}
or
var offer = Object.assign({}, element);
Read this
I have the below for loops, I have it manytime in my code, with different variables name, I would put it in a function with parameters and call it but it didn't work
for(let i = 0; i < inputs.length - 1; i++){
if(!nputs[i].value){
error += inputs[i].getAttribute('test') + " is blank";
isTrue = false;
}
}
Here what I did
let y = "";
let z = true;
function test(x,y,z){
for(let i = 0; i < x.length - 1; i++){
if(!x[i].value){
y += x[i].getAttribute('name') + " is blank !";
z = false;
}
}
}
let error = "";
let isTrue = true;
test(inputs,error,isTrue);
shall I do return in the function? if yes which return should I do?
Scope: when you define y and z outside the function (in the global scope presumably) they are different than the y and z defined in the parameter list of the function. The ones in the parameter list only exist within the body of the function. Changing the value of the parameter named y within the function does not change the value of the global variable y. So the simple answer to your question is, yes, you need to return something, since the value of the parameter y is lost when the function is done executing.
Give your variables descriptive names. Let the obfuscator do it's thing later.
function test(x,y,z) -> function valueTest(arr, err, success)
The boolean status and error string are redundant bits of information. If the error string is not empty, then the status is failure. So you don't need to return both a boolean and the string.
The status of the previous test is of no relevance to the next test. Therefore, z or success doesn't have to be passed in to the function each time, as it (or something like it) is really the desired output of the function, and each call of the function can be treated separately. If you want to combine the results from different tests then that should be the concern of whatever is calling this function - see separation of concerns and coupling
The only parameter the function actually needs is the value that is under test (the array).
When you write the function you define the return value, and thus you define how other code can decipher those results. The function itself doesn't have to do all the work of interpreting the results and building the error string. If your return value was just an array of name attribute values (of the elements of the test array that failed), the calling code could still process "success" or "failure". If the return value has one or more elements, or a length > 0 that would indicate failure.
Removing the redundant/unnecessary parameters and information, you'll have a function that looks something like this:
function valueTest(arr) {
let results = [];
for (let i = 0; i < arr.length - 1; i++){
if (!arr[i].value) {
results.push(arr[i].getAttribute('name'));
}
}
return results;
}
The caller can decipher and build an error message from that. It might make sense for the function to handle some of the additional work by returning <name> is blank! instead of just <name>, and then you just need to join the elements of the array.
...so within the function...
results.push(arr[i].getAttribute('name') + ' is blank!');
...and back in the global scope...
const error = valueTest(inputs).join(" ");
let success = error.length > 0;
5.If you want a running status indicator from different tests, evaluate an individual test's result, then logically AND that with the previous result.
const result1 = valueTest(inputs1).join(' ');
let success = results1.length > 0;
const result2 = valueTest(inputs2).join(' ');
success &= (results2.length > 0);
Seeing the issues with your code are handled in the comments, I present you a simpler method.
If you count the elements that have the attribute and are not empty and compare it to the length of all the inputs passed you will have a better test
const test = (inputs,attr) => [...inputs]
.filter(inp => inp.getAttribute(attr) && inp.value.trim() !== "").length === inputs.length;
const istrue = test(document.querySelectorAll("input"),"name")
isTrue will be true if all passed inputs has an attribute called name
You can also do
const elems = document.querySelectorAll("input[name]")
const isTrue = elems.filter(inp => inp.value.trim() !== "").length === elems.length
The process: In the game I'm making, there's a for loop that's supposed to save a value in an array. That value changes with each iteration. The problem: when the loop is done running, every element of the array is identical, all showing the most recent value.
I know this issue is common, and I've made so many different tweaks and attempts at solving it over the past 2 days.
0) I tried separating things into separate functions as much as possible.
1) I tried defining my loop counters with "let" so they would have a local scope.
2) I tried wrapping my assignment in a self-executing function so it would happen immediately, preserving the value of currentlyOn before the next loop iteration changes it. My counter is the variable c.
(function(c2, currentlyOn2) {
onAtSameTime[c2] = currentlyOn2;
return 0;
})(c, currentlyOn);
3) I tried attempt #2 with the added feature of returning a function, which still didn't save the value of currentlyOn. This option isn't a good one for me anyway, because the whole point is that I'm doing some computations ahead of time so my game will have a quick animation loop.
onAtSameTime[c] = (function(currentlyOn2) {
return function() {
return currentlyOn2;
};
})(currentlyOn);
I'm tired of beating my head against this wall. Can anyone explain what I'm doing wrong?
For more details, check out the jsfiddle I made. The problem area is at line 59, using a simple assignment:
onAtSameTime[c] = currentlyOn;
onAtSameTime[c] = currentlyOn; sets onAtSameTime[c] equal to the reference of currentlyOn, since currentlyOn is an array, not a primitive value. That reference gets updated with each iteration. You could work around that by creating a copy of the array before adding it to the onAtSameTime array. Something like onAtSameTime[c] = [].concat(currentlyOn); would do the trick.
See this fork of your JSFiddle: https://jsfiddle.net/L2by787y/
You could make a copy from currentlyOn for assigning to onAtSameTime[c]. This keeps the values, but does not keep the reference to the same array.
onAtSameTime[c] = currentlyOn.slice(); // use copy
"use strict";
function log(text) {
document.getElementById("logbox").innerHTML += JSON.stringify(text) + "<br>";
return 0;
}
function whichSwitchesAreOn() {
var currentlyOn = [],
flickedSet,
flickedOne,
turningOnCheck;
for (var c = 0; c < switchesToggled.length; c++) {
flickedSet = switchesToggled[c];
for (var d = 0; d < flickedSet.length; d++) {
flickedOne = flickedSet[d];
turningOnCheck = currentlyOn.indexOf(flickedOne);
if (turningOnCheck == -1) {
currentlyOn.push(flickedOne);
} else {
currentlyOn.splice(turningOnCheck, 1);
}
}
log("currentlyOn: " + currentlyOn);
onAtSameTime[c] = currentlyOn.slice(); // use copy
}
return 0;
}
var switchesToggled = [[0], [1, 2], [0], [2], []],
onAtSameTime = [];
whichSwitchesAreOn();
log(onAtSameTime);
<div id="logbox"></div>
You say you have tried let?
Did you have let currentlyOn = [] inside of the for loop?
for(var c = 0; c < switchesToggled.length; c++) {
let currentlyOn = [];
I am trying to make two arrays. the unique array can get the elements (no repeats) from the text array, and the counter one can count the frequency of each elements. but something is wrong with the counter one.
var unique_array=new Array();
var counter_array=new Array();
var unique=true;
for (i=0;i<text_array.length;i++){
if (unique_array.length==0){
unique_array.push(text_array[0]);
counter_array.push(1);
}
else if(unique_array.length>0&&unique_array.length<=text_array.length){
for (j=0; j<unique_array.length;j++){
if (text_array[i]==unique_array[j]){
counter_array[j]=counter_array[j]+1;// something wrong with the
alert(counter_array[j]);
var unique=false;
}
}
if (unique==true){
unique_array.push(text_array[i]);
counter_array.push[1];
}
unique=true;
}
You could also simplify the code down using a hashmap and some ES5 higher-order functions:
var text_array = ["a1","a1","a2","a3","a2","a4","a1","a5"];
var counts = {};
text_array.forEach(function(el) {
counts[el] = counts.hasOwnProperty(el) ? counts[el]+1 : 1;
});
var unique_array = Object.keys(counts);
var counter_array=unique_array.map(function(key) { return counts[key]; })
You can do this much more simply using an object. Let the values be the keys of an object, then just increment the count of each property as you go. At the end, you can get an array of the unique keys and their values:
var text_array = ['foo','bar','foo','fum','fum','foo'];
var i = text_array.length;
var obj = {};
while (i--) {
if (obj.hasOwnProperty(text_array[i])) {
obj[text_array[i]]++;
} else {
obj[text_array[i]] = 1;
}
}
console.log('Unique values: ' + Object.keys(obj)); // Unique values: foo,fum,bar
console.log('Value counts: ' + Object.keys(obj).map(function(v){return obj[v]})); // Value counts: 3,2,1
Note that the sorting of counts in the output is purely coincidental.
As Jasvir posted, you can make it pretty concise:
var obj = {};
text_array.forEach(function(v) {
obj.hasOwnProperty(v)? ++obj[v] : obj[v] = 1;
});
But the first example is a bit easier to digest.
I think the approach is what's making it difficult. A hash table / associative array would be much easier to work with.
With a hash table (an object {} in JS), you can store each word in a key and increment the value of the key when you encounter the word again. Then, at the end, just go through the hash table and gather up all the keys which have small values. Those are your unique words.
function get_unique_words(text_array) {
var hash_table, i, unique_words, keys;
hash_table = {};
for(i = 0; i < text_array.length; i++) {
if(hash_table[text_array[i]] === undefined) {
hash_table[text_array[i]] = 1;
} else {
hash_table[text_array[i]]++;
}
}
// go through the hash table and get all the unique words
unique_words = [];
keys = Object.keys(hash_table);
for(i = 0; i < keys.length; i++) {
if(hash_table[keys[i]] === 1) {
unique_words.push(keys[i]);
}
}
return unique_words.sort();
}
console.log(get_unique_words(
['blah', 'blah', 'blah', 'goose', 'duck',
'mountain', 'rock', 'paper', 'rock', 'scissors']
));
Some issues and suggestions :
Don't use var twice for the same variable.
Browsers deal with it ok, but for clarity you should only be declaring your variables once.
Always localize your loop counters - forgetting a var before your i and j will cause them to become global variables.
This is relevant when you have a page with lots of code - all global variables will show up in the debugger's watch list at all times, making it harder to debug your code.)
Use the array literal notation [] instead of the function form Array.
The function form is longer and it's easier to forget the new. It's also easier to read (IMO).
Use more whitespace (it won't bite), such as before and after an equals sign:
var x = 1;
// vs.
var x=1;
It makes the code easier to read and most people don't overdo it.
Indent your code when it's inside a block (e.g. function, if, else, while, for, etc.).
This makes it easier to read the control flow of the code and will help prevent bugs.
Use three equals signs (===) unless you are using loose equality on purpose.
This will help someone looking at your code later (probably yourself) understand better what the test is supposed to be testing.
I need to Loop in JQuery from 0 to variable-value(dynamically entered by user).How can i achieve this?
Now i am doing it by using simple For loop like this.
for( i=1; i<=fetch; i++) {
var dyndivtext = document.createElement("input");
document.body.appendChild(dyndivtext);
}
Thanks.
You could loop an empty array:
$.each(new Array(fetch), function(i) {
var dyndivtext = document.createElement("input");
document.body.appendChild(dyndivtext);
});
If you do this alot you can even fake-patch jQuery.each to take numbers:
(function($) {
var _each = $.each;
$.each = function() {
var args = $.makeArray(arguments);
if ( args.length == 2 && typeof args[0] == 'number') {
return _each.call(this, new Array(args[0]), args[1]);
}
return _each.call(this, args);
};
}(jQuery));
$.each(fetch, function(i) {
// loop
});
jQuery.each does have some great features, like the different return values inside the callback. But for a simple loop I find it much more convenient (and less overhead) to do something like:
while(fetch--) {
// loop
}
To loop between two values you should use a regular Javascript loop. The jQuery each methods are used when looping through a collection of elements or an array.
To loop from zero, you should initialise the loop variable to zero, not one. To loop from zero to the specified value, you use the <= for the comparison, but to loop from zero and the number of items as specified (i.e. from 0 to value-1), you use the < operator.
for (i = 0; i < fetch; i++) {
$('body').append($('<input/>', { type: 'text' }));
}
You mean Javascript loop.
From W3Schools:
for (var variable = startvalue; variable < endvalue; variable = variable + increment)
{
//code to be executed
}
To get the value from user and run the code you can use the following prompt.
var x=prompt("Enter the value",0);
for(i=0;i<x;i++)
{
var dyndivtext = document.createElement("input");
document.body.appendChild(dyndivtext);
}
Hope this helps.
Thanks
If you want it the full jQuery way then use that new plugin jQuery-timing. It provides inline-loops in your jQuery line:
$('body').repeat().append('<input>').until(fetch);
Nice, eh?