Related
When the page is loading for the first time, I need to check if there is an image in image_array and load the last image.
Otherwise, I disable the preview buttons, alert the user to push new image button and create an empty array to put the images;
The problem is that image_array in the else fires all time. If an array exists - it just overrides it, but alert doesn't work.
if(image_array.length > 0)
$('#images').append('<img src="'+image_array[image_array.length-1]+'" class="images" id="1" />');
else{
$('#prev_image').attr('disabled', 'true');
$('#next_image').attr('disabled', 'true');
alert('Please get new image');
var image_array = [];
}
UPDATE
Before loading html, I have something like this:
<?php if(count($images) != 0): ?>
<script type="text/javascript">
<?php echo "image_array = ".json_encode($images);?>
</script>
<?php endif; ?>
if (typeof image_array !== 'undefined' && image_array.length > 0) {
// the array is defined and has at least one element
}
Your problem may be happening due to a mix of implicit global variables and variable hoisting. Make sure you use var whenever declaring a variable:
<?php echo "var image_array = ".json_encode($images);?>
// add var ^^^ here
And then make sure you never accidently redeclare that variable later:
else {
...
image_array = []; // no var here
}
To check if an array is either empty or not
A modern way, ES5+:
if (Array.isArray(array) && array.length) {
// array exists and is not empty
}
An old-school way:
typeof array != "undefined"
&& array != null
&& array.length != null
&& array.length > 0
A compact way:
if (typeof array != "undefined" && array != null && array.length != null && array.length > 0) {
// array exists and is not empty
}
A CoffeeScript way:
if array?.length > 0
Why?
Case Undefined
Undefined variable is a variable that you haven't assigned anything to it yet.
let array = new Array(); // "array" !== "array"
typeof array == "undefined"; // => true
Case Null
Generally speaking, null is state of lacking a value. For example a variable is null when you missed or failed to retrieve some data.
array = searchData(); // can't find anything
array == null; // => true
Case Not an Array
Javascript has a dynamic type system. This means we can't guarantee what type of object a variable holds. There is a chance that we're not talking to an instance of Array.
supposedToBeArray = new SomeObject();
typeof supposedToBeArray.length; // => "undefined"
array = new Array();
typeof array.length; // => "number"
Case Empty Array
Now since we tested all other possibilities, we're talking to an instance of Array. In order to make sure it's not empty, we ask about number of elements it's holding, and making sure it has more than zero elements.
firstArray = [];
firstArray.length > 0; // => false
secondArray = [1,2,3];
secondArray.length > 0; // => true
How about (ECMA 5.1):
if(Array.isArray(image_array) && image_array.length){
// array exists and is not empty
}
This is what I use. The first condition covers truthy, which has both null and undefined. Second condition checks for an empty array.
if(arrayName && arrayName.length > 0){
//do something.
}
or thanks to tsemer's comment I added a second version
if(arrayName && arrayName.length)
Then I made a test for the second condition, using Scratchpad in Firefox:
var array1;
var array2 = [];
var array3 = ["one", "two", "three"];
var array4 = null;
console.log(array1);
console.log(array2);
console.log(array3);
console.log(array4);
if (array1 && array1.length) {
console.log("array1! has a value!");
}
if (array2 && array2.length) {
console.log("array2! has a value!");
}
if (array3 && array3.length) {
console.log("array3! has a value!");
}
if (array4 && array4.length) {
console.log("array4! has a value!");
}
which also proves that if(array2 && array2.length) and if(array2 && array2.length > 0) are exactly doing the same
optional chaining
As optional chaining proposal reached stage 4 and is getting wider support, there is a very elegant way to do this
if(image_array?.length){
// image_array is defined and has at least one element
}
You should use:
if (image_array !== undefined && image_array.length > 0)
If you want to test whether the image array variable had been defined you can do it like this
if(typeof image_array === 'undefined') {
// it is not defined yet
} else if (image_array.length > 0) {
// you have a greater than zero length array
}
JavaScript
( typeof(myArray) !== 'undefined' && Array.isArray(myArray) && myArray.length > 0 )
Lodash & Underscore
( _.isArray(myArray) && myArray.length > 0 )
You can use jQuery's isEmptyObject() to check whether the array contains elements or not.
var testArray=[1,2,3,4,5];
var testArray1=[];
console.log(jQuery.isEmptyObject(testArray)); //false
console.log(jQuery.isEmptyObject(testArray1)); //true
Source: https://api.jquery.com/jQuery.isEmptyObject/
Using undescore or lodash:
_.isArray(image_array) && !_.isEmpty(image_array)
A simple way that doesn't result in exceptions if not exist and convert to boolean:
!!array
Example:
if (!!arr) {
// array exists
}
How about this ? checking for length of undefined array may throw exception.
if(image_array){
//array exists
if(image_array.length){
//array has length greater than zero
}
}
The best is to check like:
let someArray: string[] = [];
let hasAny1: boolean = !!someArray && !!someArray.length;
let hasAny2: boolean = !!someArray && someArray.length > 0; //or like this
console.log("And now on empty......", hasAny1, hasAny2);
See full samples list:
I come across this issue quite a lot in Javascript. For me the best way to do it is to put a very broad check before checking for length. I saw some other solutions in this Q&A, but I wanted to be able to check for either null or undefined or any other false value.
if(!array || array.length == 0){
console.log("Array is either empty or does not exist")
}
This will first check for undefined, null, or other false values. If any of those are true, it will complete the boolean as this is an OR. Then the more risky check of array.length, which could error us if array is undefined, can be checked. This will never be reached if array is undefined or null, so the ordering of conditions is very important.
If you do not have a variable declared as array you can create a check:
if(x && x.constructor==Array && x.length){
console.log("is array and filed");
}else{
var x= [];
console.log('x = empty array');
}
This checks if variable x exists and if it is, checks if it is a filled array. else it creates an empty array (or you can do other stuff);
If you are certain there is an array variable created there is a simple check:
var x = [];
if(!x.length){
console.log('empty');
} else {
console.log('full');
}
You can check my fiddle here with shows most possible ways to check array.
The following is my solution wrapped in a function that also throws
errors to manage a couple of problems with object scope and all types
of possible data types passed to the function.
Here's my fiddle used to examine this problem (source)
var jill = [0];
var jack;
//"Uncaught ReferenceError: jack is not defined"
//if (typeof jack === 'undefined' || jack === null) {
//if (jack) {
//if (jack in window) {
//if (window.hasOwnP=roperty('jack')){
//if (jack in window){
function isemptyArray (arraynamed){
//cam also check argument length
if (arguments.length === 0) {
throw "No argument supplied";
}
//console.log(arguments.length, "number of arguments found");
if (typeof arraynamed !== "undefined" && arraynamed !== null) {
//console.log("found arraynamed has a value");
if ((arraynamed instanceof Array) === true){
//console.log("I'm an array");
if (arraynamed.length === 0) {
//console.log ("I'm empty");
return true;
} else {
return false;
}//end length check
} else {
//bad type
throw "Argument is not an array";
} //end type check
} else {
//bad argument
throw "Argument is invalid, check initialization";;
}//end argument check
}
try {
console.log(isemptyArray(jill));
} catch (e) {
console.log ("error caught:",e);
}
the way I found to work (comming from another language) is to make a simple function to test.
create a function that check the size of the array and pass the lenght by parameter.
isEmpty(size){
if(size==0) {
return true;
} else {
return false;
}
}
//then check
if(isEmpty(yourArray.length)==true){
//its empty
} else {
//not empty
}
You should do this
if (!image_array) {
// image_array defined but not assigned automatically coerces to false
} else if (!(0 in image_array)) {
// empty array
// doSomething
}
For me sure some of the high rated answers "work" when I put them into jsfiddle, but when I have a dynamically generated amount of array list a lot of this code in the answers just doesn't work for ME.
This is what IS working for me.
var from = [];
if(typeof from[0] !== undefined) {
//...
}
Notice, NO quotes around undefined and I'm not bothering with the length.
Probably your image_array is not array but some OBJECT with length property (like string) - try
if(image_array instanceof Array && image_array.length)
function test(image_array) {
if(image_array instanceof Array && image_array.length) {
console.log(image_array,'- it is not empty array!')
} else {
console.log(image_array,'- it is empty array or not array at all!')
}
}
test({length:5});
test('undefined');
test([]);
test(["abc"]);
In my case, array_.length always returned 0, even if it had values inside. Probably, because of non-default indexes.
So to check if array is defined we use typeof _array !== 'undefined'
And then to check if it contains any date i just simply compare it to an empty array _array !== []
in ts
isArray(obj: any)
{
return Array.isArray(obj)
}
in html
(photos == undefined || !(isArray(photos) && photos.length > 0) )
When you create your image_array, it's empty, therefore your image_array.length is 0
As stated in the comment below, i edit my answer based on this question's answer) :
var image_array = []
inside the else brackets doesn't change anything to the image_array defined before in the code
I want to add some defensive coding to the following check. I have 3 strings and I want to know if any of them have anything in them (for my purposes, null or undefined means they do not have anything in them).
if (twitterUrl.length + facebookUrl.length + linkedInUrl.length > 0) {
This works, but feels like very bulky. I use TypeScript and not sure if there is anything there that can help me with this.
if ((twitterUrl ? twitterUrl.length : 0) +
(facebookUrl ? facebookUrl.length : 0) +
(linkedInUrl ? linkedInUrl.length : 0) > 0) {
You can use the fact that empty strings are falsy¹. If you know they'll be strings or null or undefined and you don't need to worry about strings with just whitespace in them (" " is truthy¹), then:
if (twitterUrl || facebookUrl || linkedInUrl) {
If you need to worry about trimming, then a helper function is probably in order:
function present(s) {
return s && (typeof s !== "string" || s.trim());
}
and
if (present(twitterUrl) || present(facebookUrl) || present(linkedInUrl)) {
or
if ([twitterUrl, facebookUrl, linkedInUrl].some(present)) {
¹ falsy and truthy: When you use a value in a condition (like an if), JavaScript will implicitly coerce the value to a boolean. A value that coerces to false is falsy; one that coerces to true is truthy. The falsy values are "", null, undefined, 0, NaN, and of course, false. All other values (including " ") are truthy.
You could define a function as the following one:
function getLength(s){
if(typeof s !== "string") return 0;
return s.length;
}
and then use it like below:
if (getLength(twitterUrl) > 0 || getLenght(facebookUrr) > 0 || getLength(linkedInUrl){
// code
}
Essentially, getLength check if the value you pass when you call the function is a string and if so it returns its length. Otherwise, it returns 0. So in order to achieve that you want, (I want to know if any of them have anything in them), you have to check one by one the strings you have, if the first string has a length greater than zero, there isn't any need to continue the check for the other two strings. Otherwise you call the function on the second string and so on and so forth.
Try like this, normal if statement also works
const socialLinks = [twitterUrl, facebookUrl, linkedInUrl];
const hasSomething = socialLinks.some(social => social);
Here is falsy value like null, undefined, '' and etc., https://developer.mozilla.org/en-US/docs/Glossary/Falsy
if social are empty string('') or null or undefined then it's return false. We omitted return keyword because arrow function has implicit return behaviour.
This is a solution using some(), which checks whether at least one element in the array passes the test implemented by the provided function.
var twitterUrl, facebookUrl, linkedInUrl;
linkedInUrl = 'nonEmpty';
result = [twitterUrl, facebookUrl, linkedInUrl].some(arrVal => arrVal);
console.log(result);
Is there any check if a value is not null and not empty string in Javascript? I'm using the following one:
var data; //get its value from db
if(data != null && data != '') {
// do something
}
But I'm wondering if there is another better solution. Thanks.
If you truly want to confirm that a variable is not null and not an empty string specifically, you would write:
if(data !== null && data !== '') {
// do something
}
Notice that I changed your code to check for type equality (!==|===).
If, however you just want to make sure, that a code will run only for "reasonable" values, then you can, as others have stated already, write:
if (data) {
// do something
}
Since, in javascript, both null values, and empty strings, equals to false (i.e. null == false).
The difference between those 2 parts of code is that, for the first one, every value that is not specifically null or an empty string, will enter the if. But, on the second one, every true-ish value will enter the if: false, 0, null, undefined and empty strings, would not.
Instead of using
if(data !== null && data !== '' && data!==undefined) {
// do something
}
You can use below simple code
if(Boolean(value)){
// do something
}
Values that are intuitively “empty”, like 0, an empty string, null, undefined, and NaN, become false
Other values become true
Both null and an empty string are falsy values in JS. Therefore,
if (data) { ... }
is completely sufficient.
A note on the side though: I would avoid having a variable in my code that could manifest in different types. If the data will eventually be a string, then I would initially define my variable with an empty string, so you can do this:
if (data !== '') { ... }
without the null (or any weird stuff like data = "0") getting in the way.
if (data?.trim().length > 0) {
//use data
}
the ?. optional chaining operator will short-circuit and return undefined if data is nullish (null or undefined) which will evaluate to false in the if expression.
I often test for truthy value and also for empty spaces in the string:
if(!(!data || data.trim().length === 0)) {
// do something here
}
If you have a string consisting of one or more empty spaces it will evaluate to true.
Simple solution to check if string is undefined or null or "":-
const value = null;
if(!value) {
console.log('value is either null, undefined or empty string');
}
Both null and empty could be validated as follows:
<script>
function getName(){
var myname = document.getElementById("Name").value;
if(myname != '' && myname != null){
alert("My name is "+myname);
}else{
alert("Please Enter Your Name");
}
}
try it----------
function myFun(){
var inputVal=document.getElementById("inputId").value;
if(inputVal){
document.getElementById("result").innerHTML="<span style='color:green'>The value is "+inputVal+'</span>';
}
else{
document.getElementById("result").innerHTML="<span style='color:red'>Something error happen! the input May be empty.</span>";
}
}
<input type="text" id="inputId">
<input type="button" onclick="myFun()" value="View Result">
<h1 id="result"></h1>
I got so fed up with checking for null and empty strings specifically, that I now usually just write and call a small function to do it for me.
/**
* Test if the given value equals null or the empty string.
*
* #param {string} value
**/
const isEmpty = (value) => value === null || value === '';
// Test:
isEmpty(''); // true
isEmpty(null); // true
isEmpty(1); // false
isEmpty(0); // false
isEmpty(undefined); // false
When we code empty in essence could mean any one of the following given the circumstances;
0 as in number value
0.0 as in float value
'0' as in string value
'0.0' as in string value
null as in Null value, as per chance it could also capture undefined or it may not
undefined as in undefined value
false as in false truthy value, as per chance 0 also as truthy but what if we want to capture false as it is
'' empty sting value with no white space or tab
' ' string with white space or tab only
In real life situation as OP stated we may wish to test them all or at times we may only wish to test for limited set of conditions.
Generally if(!a){return true;} serves its purpose most of the time however it will not cover wider set of conditions.
Another hack that has made its round is return (!value || value == undefined || value == "" || value.length == 0);
But what if we need control on whole process?
There is no simple whiplash solution in native core JavaScript it has to be adopted. Considering we drop support for legacy IE11 (to be honest even windows has so should we) below solution born out of frustration works in all modern browsers;
function empty (a,b=[])
{if(!Array.isArray(b)) return;
var conditions=[null,'0','0.0',false,undefined,''].filter(x => !b.includes(x));
if(conditions.includes(a)|| (typeof a === 'string' && conditions.includes(a.toString().trim())))
{return true;};
return false;};`
Logic behind the solution is function has two parameters a and b, a is value we need to check, b is a array with set conditions we need to exclude from predefined conditions as listed above. Default value of b is set to an empty array [].
First run of function is to check if b is an array or not, if not then early exit the function.
next step is to compute array difference from [null,'0','0.0',false,undefined,''] and from array b. if b is an empty array predefined conditions will stand else it will remove matching values.
conditions = [predefined set] - [to be excluded set]
filter function does exactly that make use of it.
Now that we have conditions in array set all we need to do is check if value is in conditions array.
includes function does exactly that no need to write nasty loops of your own let JS engine do the heavy lifting.
Gotcha
if we are to convert a into string for comparison then 0 and 0.0 would run fine however Null and Undefined would through error blocking whole script. We need edge case solution. Below simple || covers the edge case if first condition is not satisfied. Running another early check through include makes early exit if not met.
if(conditions.includes(a)|| (['string', 'number'].includes(typeof a) && conditions.includes(a.toString().trim())))
trim() function will cover for wider white spaces and tabs only value and will only come into play in edge case scenario.
Play ground
function empty (a,b=[]){
if(!Array.isArray(b)) return;
conditions=[null,'0','0.0',false,undefined,''].filter(x => !b.includes(x));
if(conditions.includes(a)||
(['string', 'number'].includes(typeof a) && conditions.includes(a.toString().trim()))){
return true;
}
return false;
}
console.log('1 '+empty());
console.log('2 '+empty(''));
console.log('3 '+empty(' '));
console.log('4 '+empty(0));
console.log('5 '+empty('0'));
console.log('6 '+empty(0.0));
console.log('7 '+empty('0.0'));
console.log('8 '+empty(false));
console.log('9 '+empty(null));
console.log('10 '+empty(null,[null]));
console.log('11 dont check 0 as number '+empty(0,['0']));
console.log('12 dont check 0 as string '+empty('0',['0']));
console.log('13 as number for false as value'+empty(false,[false]));
Lets make it complex - what if our value to compare is array its self and can be as deeply nested it can be. what if we are to check if any value in array is empty, it can be an edge business case.
function empty (a,b=[]){
if(!Array.isArray(b)) return;
conditions=[null,'0','0.0',false,undefined,''].filter(x => !b.includes(x));
if(Array.isArray(a) && a.length > 0){
for (i = 0; i < a.length; i++) { if (empty(a[i],b))return true;}
}
if(conditions.includes(a)||
(['string', 'number'].includes(typeof a) && conditions.includes(a.toString().trim()))){
return true;
}
return false;
}
console.log('checking for all values '+empty([1,[0]]));
console.log('excluding for 0 from condition '+empty([1,[0]], ['0']));
it simple and wider use case function that I have adopted in my framework;
Gives control over as to what exactly is the definition of empty in a given situation
Gives control over to redefine conditions of empty
Can compare for almost for every thing from string, number, float, truthy, null, undefined and deep arrays
Solution is drawn keeping in mind the resuability and flexibility. All other answers are suited in case if simple one or two cases are to be dealt with. However, there is always a case when definition of empty changes while coding above snippets make work flawlessly in that case.
function validateAttrs(arg1, arg2, arg3,arg4){
var args = Object.values(arguments);
return (args.filter(x=> x===null || !x)).length<=0
}
console.log(validateAttrs('1',2, 3, 4));
console.log(validateAttrs('1',2, 3, null));
console.log(validateAttrs('1',undefined, 3, 4));
console.log(validateAttrs('1',2, '', 4));
console.log(validateAttrs('1',2, 3, null));
When the page is loading for the first time, I need to check if there is an image in image_array and load the last image.
Otherwise, I disable the preview buttons, alert the user to push new image button and create an empty array to put the images;
The problem is that image_array in the else fires all time. If an array exists - it just overrides it, but alert doesn't work.
if(image_array.length > 0)
$('#images').append('<img src="'+image_array[image_array.length-1]+'" class="images" id="1" />');
else{
$('#prev_image').attr('disabled', 'true');
$('#next_image').attr('disabled', 'true');
alert('Please get new image');
var image_array = [];
}
UPDATE
Before loading html, I have something like this:
<?php if(count($images) != 0): ?>
<script type="text/javascript">
<?php echo "image_array = ".json_encode($images);?>
</script>
<?php endif; ?>
if (typeof image_array !== 'undefined' && image_array.length > 0) {
// the array is defined and has at least one element
}
Your problem may be happening due to a mix of implicit global variables and variable hoisting. Make sure you use var whenever declaring a variable:
<?php echo "var image_array = ".json_encode($images);?>
// add var ^^^ here
And then make sure you never accidently redeclare that variable later:
else {
...
image_array = []; // no var here
}
To check if an array is either empty or not
A modern way, ES5+:
if (Array.isArray(array) && array.length) {
// array exists and is not empty
}
An old-school way:
typeof array != "undefined"
&& array != null
&& array.length != null
&& array.length > 0
A compact way:
if (typeof array != "undefined" && array != null && array.length != null && array.length > 0) {
// array exists and is not empty
}
A CoffeeScript way:
if array?.length > 0
Why?
Case Undefined
Undefined variable is a variable that you haven't assigned anything to it yet.
let array = new Array(); // "array" !== "array"
typeof array == "undefined"; // => true
Case Null
Generally speaking, null is state of lacking a value. For example a variable is null when you missed or failed to retrieve some data.
array = searchData(); // can't find anything
array == null; // => true
Case Not an Array
Javascript has a dynamic type system. This means we can't guarantee what type of object a variable holds. There is a chance that we're not talking to an instance of Array.
supposedToBeArray = new SomeObject();
typeof supposedToBeArray.length; // => "undefined"
array = new Array();
typeof array.length; // => "number"
Case Empty Array
Now since we tested all other possibilities, we're talking to an instance of Array. In order to make sure it's not empty, we ask about number of elements it's holding, and making sure it has more than zero elements.
firstArray = [];
firstArray.length > 0; // => false
secondArray = [1,2,3];
secondArray.length > 0; // => true
How about (ECMA 5.1):
if(Array.isArray(image_array) && image_array.length){
// array exists and is not empty
}
This is what I use. The first condition covers truthy, which has both null and undefined. Second condition checks for an empty array.
if(arrayName && arrayName.length > 0){
//do something.
}
or thanks to tsemer's comment I added a second version
if(arrayName && arrayName.length)
Then I made a test for the second condition, using Scratchpad in Firefox:
var array1;
var array2 = [];
var array3 = ["one", "two", "three"];
var array4 = null;
console.log(array1);
console.log(array2);
console.log(array3);
console.log(array4);
if (array1 && array1.length) {
console.log("array1! has a value!");
}
if (array2 && array2.length) {
console.log("array2! has a value!");
}
if (array3 && array3.length) {
console.log("array3! has a value!");
}
if (array4 && array4.length) {
console.log("array4! has a value!");
}
which also proves that if(array2 && array2.length) and if(array2 && array2.length > 0) are exactly doing the same
optional chaining
As optional chaining proposal reached stage 4 and is getting wider support, there is a very elegant way to do this
if(image_array?.length){
// image_array is defined and has at least one element
}
You should use:
if (image_array !== undefined && image_array.length > 0)
If you want to test whether the image array variable had been defined you can do it like this
if(typeof image_array === 'undefined') {
// it is not defined yet
} else if (image_array.length > 0) {
// you have a greater than zero length array
}
JavaScript
( typeof(myArray) !== 'undefined' && Array.isArray(myArray) && myArray.length > 0 )
Lodash & Underscore
( _.isArray(myArray) && myArray.length > 0 )
You can use jQuery's isEmptyObject() to check whether the array contains elements or not.
var testArray=[1,2,3,4,5];
var testArray1=[];
console.log(jQuery.isEmptyObject(testArray)); //false
console.log(jQuery.isEmptyObject(testArray1)); //true
Source: https://api.jquery.com/jQuery.isEmptyObject/
Using undescore or lodash:
_.isArray(image_array) && !_.isEmpty(image_array)
A simple way that doesn't result in exceptions if not exist and convert to boolean:
!!array
Example:
if (!!arr) {
// array exists
}
How about this ? checking for length of undefined array may throw exception.
if(image_array){
//array exists
if(image_array.length){
//array has length greater than zero
}
}
The best is to check like:
let someArray: string[] = [];
let hasAny1: boolean = !!someArray && !!someArray.length;
let hasAny2: boolean = !!someArray && someArray.length > 0; //or like this
console.log("And now on empty......", hasAny1, hasAny2);
See full samples list:
I come across this issue quite a lot in Javascript. For me the best way to do it is to put a very broad check before checking for length. I saw some other solutions in this Q&A, but I wanted to be able to check for either null or undefined or any other false value.
if(!array || array.length == 0){
console.log("Array is either empty or does not exist")
}
This will first check for undefined, null, or other false values. If any of those are true, it will complete the boolean as this is an OR. Then the more risky check of array.length, which could error us if array is undefined, can be checked. This will never be reached if array is undefined or null, so the ordering of conditions is very important.
If you do not have a variable declared as array you can create a check:
if(x && x.constructor==Array && x.length){
console.log("is array and filed");
}else{
var x= [];
console.log('x = empty array');
}
This checks if variable x exists and if it is, checks if it is a filled array. else it creates an empty array (or you can do other stuff);
If you are certain there is an array variable created there is a simple check:
var x = [];
if(!x.length){
console.log('empty');
} else {
console.log('full');
}
You can check my fiddle here with shows most possible ways to check array.
The following is my solution wrapped in a function that also throws
errors to manage a couple of problems with object scope and all types
of possible data types passed to the function.
Here's my fiddle used to examine this problem (source)
var jill = [0];
var jack;
//"Uncaught ReferenceError: jack is not defined"
//if (typeof jack === 'undefined' || jack === null) {
//if (jack) {
//if (jack in window) {
//if (window.hasOwnP=roperty('jack')){
//if (jack in window){
function isemptyArray (arraynamed){
//cam also check argument length
if (arguments.length === 0) {
throw "No argument supplied";
}
//console.log(arguments.length, "number of arguments found");
if (typeof arraynamed !== "undefined" && arraynamed !== null) {
//console.log("found arraynamed has a value");
if ((arraynamed instanceof Array) === true){
//console.log("I'm an array");
if (arraynamed.length === 0) {
//console.log ("I'm empty");
return true;
} else {
return false;
}//end length check
} else {
//bad type
throw "Argument is not an array";
} //end type check
} else {
//bad argument
throw "Argument is invalid, check initialization";;
}//end argument check
}
try {
console.log(isemptyArray(jill));
} catch (e) {
console.log ("error caught:",e);
}
the way I found to work (comming from another language) is to make a simple function to test.
create a function that check the size of the array and pass the lenght by parameter.
isEmpty(size){
if(size==0) {
return true;
} else {
return false;
}
}
//then check
if(isEmpty(yourArray.length)==true){
//its empty
} else {
//not empty
}
You should do this
if (!image_array) {
// image_array defined but not assigned automatically coerces to false
} else if (!(0 in image_array)) {
// empty array
// doSomething
}
For me sure some of the high rated answers "work" when I put them into jsfiddle, but when I have a dynamically generated amount of array list a lot of this code in the answers just doesn't work for ME.
This is what IS working for me.
var from = [];
if(typeof from[0] !== undefined) {
//...
}
Notice, NO quotes around undefined and I'm not bothering with the length.
Probably your image_array is not array but some OBJECT with length property (like string) - try
if(image_array instanceof Array && image_array.length)
function test(image_array) {
if(image_array instanceof Array && image_array.length) {
console.log(image_array,'- it is not empty array!')
} else {
console.log(image_array,'- it is empty array or not array at all!')
}
}
test({length:5});
test('undefined');
test([]);
test(["abc"]);
In my case, array_.length always returned 0, even if it had values inside. Probably, because of non-default indexes.
So to check if array is defined we use typeof _array !== 'undefined'
And then to check if it contains any date i just simply compare it to an empty array _array !== []
in ts
isArray(obj: any)
{
return Array.isArray(obj)
}
in html
(photos == undefined || !(isArray(photos) && photos.length > 0) )
When you create your image_array, it's empty, therefore your image_array.length is 0
As stated in the comment below, i edit my answer based on this question's answer) :
var image_array = []
inside the else brackets doesn't change anything to the image_array defined before in the code
I don't recollect exactly what its called but php checks and exists as soon as it finds one false value in a function, like so :
// php
if(isset(a["hi"]) && isset(a["hi"]["hello"])) {
}
here if a["hi"] is not set, it will not bother to check the next a["hi"]["hello"].
to check something like this in javascript you'd need to nest
// js
if(typeof(a["hi"]) != "undefined") {
if(typeof(a["hi"]["hello"]) != "undefined") {
}
}
Can we do php style lazy checking in javascript?
(I may not be using the best method to check if an element exists in a multi-dimentional array, if there is a succinct way of doing this, would love to know.)
thanks!
You could use in to check property existence.
if(a && ('hi' in a) && ('hello' in a['hi'])) {
}
if(a.hi === undefined && a.hi.hello === undefined) {
if you know that a.hi can never be a falsey value (null / false / 0) you can do
if(!a.hi && !a.hi.hello) {
Checking the typeof a variable for the string "undefined" is equivalent to using === to check whether the variable is the same data type as the undefined keyword. You can therefore reduce the nested if statements to a single statement:
if(a.hi !== undefined && a.hi.hello !== undefined) {
// do something with a.hi.hello
}
It's worth noting that the statement above assumes that a is not null when the if statement takes place which could cause errors. It also holds true that if you require a.hi.hello to be present for the if statement to evaluate, then you can use falsy checking for a and a.hi as they would need to be object types for (which are non-falsy):
if(!!a && a.hi && a.hi.hello !== undefined) {
// do something with a.hi.hello
}