I can't seem to figure out this problem. I need to iterate over some objects, as of right now, named column_1, column_2, column_3 and column_4.
How do i use the i variable, to get the correct object?
This is my code right now, which isn't working...
for (var i = 1; i < layouts.columns; i++) {
console.log(layouts.column_[i]);
}
Do you mean you need to iterate over the properties of an object?
It's not like an array. You have to do something like
let keys = Object.keys(layouts.columns);
for(var i = 0; i < keys.length -1; i ++ ) {// do stuff};
or
for (var key in layouts.columns) {
var column = layouts.columns[key];
}
Or like others have mentioned, if all property names are column_x, you could loop through 4, and access like layouts['column_'+i]
Related
I have the following JavaScript code fragment
var ip = new Array();
// This array filled with values and passed to function
function calculateTime(ip) {
for (i in ip) {
window.alert(i);
if (!i in myArray) {
myArray[i] = 0;
} else {
myArray[i] += 1;
}
}
}
I expect i to be an index (0, 1, 2 ...) but sometimes window.alert prints "arrayIndex" and because of that my code doesn't work correctly. Can someone explain me the reason? I am new in JavaScript.
for in will loop over all the enumerable properties of an object.
None of the properties that come with an array are enumerable in modern browsers, but any that are added (such as the normal array indexes or any custom named properties) will be.
Somewhere you have some code that is adding an arrayIndex property to your array and it is coming up when you loop over it.
var myArray = [];
myArray[0] = 1;
myArray[1] = 1;
myArray[2] = 1;
myArray.arrayIndex = 1;
for (prop in myArray) {
console.log(prop);
}
If you only want to get numerical indexes, then use a standard for loop.
for (var i = 0 ; i < myArray.length ; i++) {
console.log(i);
}
For arrays, you should use a numeric variable rather than in:
for(var i = 0; i < ip.length; i++)
in is to iterate over the keys of an Object, but even there you have to take much care to filter out inherited properties.
Now, since arrays are objects too in JavaScript, you can assign them object properties:
ip["arrayIndex"] = 'some value';
Then "arrayIndex" will show up in a for...in iteration, whereas in a "normal" for loop, it won't.
Use either
for(var i=0; i<ip.length; i++){
//your code
}
or
ip.forEach(function(val,i){
// your code
});
The for(var x in y) loop works best for Object rather than Array. When you use it on arrays it will loop through all properties including named ones like length not just numerical indices.
I have an array of objects, i was trying to iterate over. The array is pretty simple in format.
{a:5, b:"key", c:19}
i was trying to compare an array with a subset, say: [{a:5},...]
for (var i = 0; i < subset.length; i++) {
var searchTerm = subset[i].a;
var index = objs.indexOf(searchTerm, function (el) {
return el.a;
});
if (index > -1) {
objs[index].Found = true;
}
}
So that way ultimately objs, could have a new key in it, 'Found'
This way, it will set the main array objs item.Found = true, if it existed in subset.
There are 2 issues though. Accounting for multiple instances of the same item, and the fact that this current implementation doesnt seem to work.
This is a slight expansion of (indexOf method in an object array? )but with an array of search terms.
ideally, i dont want to change the arrays at all, so im trying not to slice, etc.
In a lot of the defintions, indexOf is defined as:
function indexOf (key, start);
instead of the ideas i am trying to work with.
Edit
Here is some code that i have to get this working, but i was thinking there is a more effecient way to do it than written.
for (var j = 0; j < compare.length; j++){
var searchTerm = compare[j]["a"];
for (var k = 0; k < objs.length; k++){
if (!objs[k].Found && objs[k]["a"] == searchTerm){
objs[k].Found = true;
break;
}
}
}
I want to make a loop that makes arrays automatically and assign the values to it.
The problem is how to generate the array itself automatically.
for(var attGetter=1; attGetter <= num; attGetter++){
var catesArray1 = new Array();
for(var atttGetterArray=1; atttGetterArray <= series; attGetterArray++){
idOfInput = "cate"+chartGetter+"_series"+attGetterArray;
catesArray1.push($("#"+idOfInput).val());
}
}
I want the loop to generate the array itself automatically like
catesArray1
catesArray2
catesArray3
and so on..
You need an object or an array to hold the multiple arrays you wish to create. Maybe something you are looking for is like the following?
var arrayHolder = new Array();
for(var attGetter=1; attGetter <= num; attGetter++){
var catesArray = new Array();
for(var attGetterArray=1; atttGetterArray <= series; attGetterArray++){
idOfInput = "cate"+chartGetter+"_series"+attGetterArray;
catesArray.push($("#"+idOfInput).val());
}
arrayHolder.push(catesArray);
}
If you want the arrays to be in global namespace, You can try
window['catesArray' + attGetter] = [];
...
window['catesArray' + attGetter].push(...)
Else you can create a hash object and use it to hold the reference
var obj = {};
.....
obj['catesArray' + attGetter] = [];
.....
obj['catesArray' + attGetter].push(...)
In that case you will have to create one new array that holds all the cacatesArrays from first for loop
var catesArrayContainer = new Array(); //<<<---------------------
for(var attGetter=1; attGetter <= num; attGetter++){
var catesArray = new Array();
for(var atttGetterArray=1; atttGetterArray <= series; attGetterArray++){
idOfInput = "cate"+chartGetter+"_series"+attGetterArray;
catesArray.push($("#"+idOfInput).val());
}
catesArrayContainer.push(catesArray); //<<<--------------------
}
EDIT :
This happens because the scope of variable catesArray1 was limited. When the loop enters next iteration the catesArray1 gets reinitialized, thus losing all the previously stored values...
Now in the code I have posted, we are storing every instance of catesArray1 in another array, and your values persist out side of the for loop
You can do something like this for 4 arrays of 5 elements each
yourarray=[];
for (i = 0; i <4; i++) {
temparray=[];
for (j = 0; j < 5; j++) {
temparray.push($('#'+whateverID+'_'+i+'_'+j)) //your values here
}
yourarray.push(temparray);
}
Check it on this JSFiddle. open chrome console to see array
If you want to create array within loop from index
You can use eval to evaluate javascript from strings but i wont use that unless there is no other way. you can see both above and eval method in this Fiddle. Open Chrome console to see array values
Just a comparison of using eval and 2D array
Open console in chrome while you run this jsFiddle and you will see the difference in eval and 2darray in context of this question.
You should assign them to an object. In this case, make an object variable before the first for-loop to hold all arrays:
var allArrays = {};
for(var attGetter=1; attGetter <= num; attGetter++){
var currentArray = allArrays['catesArray' + attGetter] = new Array();
for(var atttGetterArray=1; atttGetterArray <= series; attGetterArray++){
idOfInput = "cate"+chartGetter+"_series"+attGetterArray;
currentArray.push($("#"+idOfInput).val());
}
}
Instead of attempting to create & allocate dynamically named variables, I would think of this more of an array of array's if you will. In other words, create an array that holds all of the arrays you want:
var collections = []; // Literal notation for creating an array in JS
From here, it's a matter of making each value you create within this array its own array:
var n = 10; // Total amount of arrays you want
for (var i = 0; i < n; i++) {
var values = [];
// Have another loop that fills in the values array as expected
collections.push(values); // Each element at collections[i] is its own array.
}
If you truly need named elements, you could potentially do something very similar with just an object {} instead, and refer to each element by a name you create.
var collections = {}; // Literal notation for an object in JS
var n = 10; // Total amount of arrays you want
for (var i = 0; i < n; i++) {
var values = []; // Literal notation for an array in JS
// Fill in the values array as desired
var name = 'arr' + i; // How you'll refer to it in the object
collections[name] = values;
}
I suggest the former though, since it does not sound like you need to have explicit names on your arrays, but just want multiple layers of arrays.
am trying to loop and get the values of names from this array , but am not able..really frustrated with javascript
can anyone please help and guide me to do this and for more complex arrays.. i cant seem to find and tutorial good to show examples of this
thank you , here is the code
var object={name:'angelos',name:'nick',name:'maria'};
var i;
for (i = 0; i < object.length; i += 1) {
document.writeln(object[name][i]);
}
That's an object, not an array. You can make it a simple array instead:
var arr = ['angelos', 'nick', 'maria'];
for (var i = 0; i < arr.length; i++) {
document.writeln(arr[i]);
}
Or, if you want to have objects inside the array (not needed if every object has just one key):
var arr = [{name: 'angelos'}, {name: 'nick'}, {name: 'maria'}];
for (var i = 0; i < arr.length; i++) {
document.writeln(arr[i].name);
}
First of all, your object has duplicate keys name. This is poor code and will throw an error in strict mode.
I would also use either a for ... in loop or Array.forEach here, because much less code is required to implement the desired effect.
Seems like you need to use an Array:
var arr = ["nick", "maria", "chaz"];
arr.forEach(function (name) {
document.writeln(name);
});
You can use Array.forEach, which passes in each index to an anonymous function.
Alternatively, if you wanted each person to be an Object:
var people = [{name: 'chaz', title: 'mr'}, {name: 'nick', title: 'mr'}, {name: 'maria',title: 'ms'}];
for (i in people) {
if (!people.hasOwnProperty(i)) { continue; }
var person = people[i];
document.writeln(person.name);
}
References
Take a look at Array.forEach here
A good reference on for ... in loops here
You can put your data in an array and fill it with objects containing a name attribute (and others e.g. adress or so, if you like to)
http://jsfiddle.net/5NK6x/
var obj=[{name:'angelos'}, {name:'nick'}, {name:'maria'}],
i;
for (i = 0; i < obj.length; i += 1) {
document.write(' ' + obj[i]['name']);
}
First of all, that is an object, not an array. You probably meant to have an array of objects. I'm saying that because you have three keys all called name. Keys must be unique. like this:
var people = [{name: 'angelos'}, {name:'nick'}, {name:'maria'}];
In that case you would loop through like this:
for (var i = 0; i < people.length; i++) {
document.writeln(people[i].name);
}
Example: http://jsfiddle.net/lbstr/cMqaH/
This is a mix between an array and JSON. If your data looked like this:
var object = [{"name":"angelos"},{"name":"nick"},{"name":"maria"}];
You'd be able to access the elements like so:
for(var i=0,i<object.length,i++)
{
alert(object[i].name);
}
I'm using a javascript associative array (arr) and am using this method to loop through it.
for(var i in arr) {
var value = arr[i];
alert(i =") "+ value);
}
The problem is that the order of the items is important to me, and it needs to loop through from last to first, rather than first to last as it currently does.
Is there a way to do this?
Four things:
JavaScript has arrays (integer-indexed [see comments below]) and objects (string-indexed). What you would call an associative array in another language is called an object in JS.
You shouldn't use for in to loop through a JS array.
If you're looping through an object, use: hasOwnProperty.
JavaScript doesn't guarantee the order of keys in an object. If you care about order, use an array instead.
If you're using a normal array, do this:
for (var i = arr.length - 1; i >= 0; i--) {
//do something with arr[i]
}
Warning: this answer is ancient.
If you're here for a quick fix, kindly refer to the much better answer below.
Original answer retained, because reasons. See comments.
Using a temporary array holding the keys in reverse order:
var keys = new Array();
for (var k in arr) {
keys.unshift(k);
}
for (var c = keys.length, n = 0; n < c; n++) {
alert(arr[keys[n]]);
}
For a normal array, I would have done this:
var i = arr.length;
while (i--) {
var value = arr[i];
alert(i =") "+ value);
}
This is faster than a "for" loop.
http://blogs.oracle.com/greimer/entry/best_way_to_code_a
In modern browsers you can now use Object.keys to get your array of properties and step through it in reverse order, allowing you to skip the preliminary key collection loop.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys
var keys = Object.keys(subject);
for (var i = keys.length-1; i >= 0; i--) {
var k = keys[i],
v = subject[k];
console.log(k+":",v);
}