Check if an array is empty or exists

user_1564141 0
Viewed 1362147

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; ?>
arrays jquery javascript
23 Answers

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

}
user_32629830

JavaScript

( typeof(myArray) !== 'undefined' && Array.isArray(myArray) && myArray.length > 0 )

Lodash & Underscore

( _.isArray(myArray) && myArray.length > 0 )
user_8365510

A simple way that doesn't result in exceptions if not exist and convert to boolean:

!!array

Example:

if (!!arr) {
  // array exists
}
user_5301970

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: code sample results

user_66295150

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);
}
user_6089910

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"]);

user_8600990

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 !== []

user_115877290

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
        }
user_89450780

in ts

 isArray(obj: any) 
{
    return Array.isArray(obj)
  }

in html

(photos == undefined || !(isArray(photos) && photos.length > 0) )

user_102034320
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