JavaScript Isset() Equivalent

JavaScript isset() equivalent

I generally use the typeof operator:

if (typeof obj.foo !== 'undefined') {
  // your code here
}

It will return "undefined" either if the property doesn't exist or its value is undefined.

_{(See also: Difference between undefined and not being defined.)}

There are other ways to figure out if a property exists on an object, like the hasOwnProperty method:

if (obj.hasOwnProperty('foo')) {
  // your code here
}

And the in operator:

if ('foo' in obj) {
  // your code here
}

The difference between the last two is that the hasOwnProperty method will check if the property exist physically on the object (the property is not inherited).

The in operator will check on all the properties reachable up in the prototype chain, e.g.:

var obj = { foo: 'bar'};

obj.hasOwnProperty('foo'); // true
obj.hasOwnProperty('toString'); // false
'toString' in obj; // true

As you can see, hasOwnProperty returns false and the in operator returns true when checking the toString method, this method is defined up in the prototype chain, because obj inherits form Object.prototype.

php isset() equivalent in javascript

ECMAScript defines the hasOwnProperty method for checking if an object has a property of a given name:

var foo = {'bar':'bar'}

alert( foo.hasOwnProperty( 'bar' ) ); //true
alert( foo.hasOwnProperty( 'baz' ) ); //false

EDIT: This doesn't fully answer your question

It's possible for a property to be set as undefined

foo.bar = undefined;

alert( foo.hasOwnProperty( 'bar' ) ); //still true

The important question is: What do you need your truth table to be?

In php:

type  | isset() | == true
------+---------+----------
null  | false   | false
false | true    | false
true  | true    | true
""    | true    | false
"a"   | true    | true
0     | true    | false
1     | true    | true

In JS:

type      | isset() | truthy
----------+---------+--------
NaN       | ?       | false
undefined | ?       | false
null      | false   | false
true      | true    | true
false     | true    | false
""        | true    | false
"a"       | true    | true
0         | true    | false
1         | true    | true

JavaScript isset() function

When javascript variables are not declared and you try to call them, they return undefined, so you can do:

if (typeof sessionvalue == "undefined" || sessionvalue == null)

PHP if (isset) JavaScript equivalent

Just remove the empty() function, as that is invalid JS. With that said, here is you adjusted code:

$.ajax({
    type: 'get',
    url: url,
    success: function (data) {
        if (data[0] != null) {
            console.log('has data');
        } else {
            console.log('does not have data');
        }
    }
});

is there something like isset of php in javascript/jQuery?

Try this expression:

typeof(variable) != "undefined" && variable !== null

This will be true if the variable is defined and not null, which is the equivalent of how PHP's isset works.

You can use it like this:

if(typeof(variable) != "undefined" && variable !== null) {
    bla();
}

What is the equivalent of isset($_POST['name']) in javascript?

First don't forget that you need name attributes on your checkboxes for PHP. Second, although your ids are valid in HTML5, I'd change them to start with a letter to make them HTML4 compatible.

I print the POST variable using php and assign it to post in javascript. Then I check if the checkbox exists in the post variable.

page1.php:

<form method="POST" action="page2.php">
<input type="checkbox" id="1" name="box1">
<input type="checkbox" id="2" name="box2">
<input type="checkbox" id="3" name="box3">
<input type="checkbox" id="4" name="box4">
<input type="checkbox" id="5" name="box5">
<input type="checkbox" id="6" name="box6">
<input type="submit">
</form>

page2.php:

<form method="POST" action="action.php">
<input type="checkbox" id="1">
<input type="checkbox" id="2">
<input type="checkbox" id="3">
<input type="checkbox" id="4">
<input type="checkbox" id="5">
<input type="checkbox" id="6">
<input type="submit">
</form>

<script>
var post = <?php echo json_encode($_POST) ?>;
if (!post.box2) document.getElementById("4").disabled = true;

</script>

isset equivalent in javascript to find palindrome

First, thank you for all the comments.

Second, I ran a var_dump on the count array in the PHP file and this was the result:

array (size=2)
'm' => int 2
'o' => int 1

Which lead me to understand that count in js has to be an object for this work and I would have to create indexes of the object, depending on the string entered.

One thing lead to another and a complete re-write, but it works, along with a spell checker - see link at the bottom for complete code:

var count = {};
var strArr = [];
var oddCounter = 0;
var objKeys = [];
var splitString;
var reverseArray;
var joinArray;
var url = "test-spelling.php";
var someRes = "";

var mForN = function(obj, strArr) {
  for (var y = 0; y < strArr.length; y++) {
    // console.log("obj[strArr[" + y + "]]: " + obj[strArr[y]]);
    if (isset(obj[strArr[y]])) {
      obj[strArr[y]]++;
    } else {
      obj[strArr[y]] = 1;
    }
  }
  return obj;
};

var mForN_2 = function(obj, objKeys) {
  for (var z = 0; z < objKeys.length; z++) {
    /* console.log(
      "obj[objKeys[z]]: " +
        obj[objKeys[z]] +
        " obj[objKeys[z]] % 2: " +
        eval(obj[objKeys[z]] % 2)
    ); */
    if (eval(obj[objKeys[z]] % 2) == 1) {
      oddCounter++;
    }
    // console.log("oddCounter: " + oddCounter);
  }

  return oddCounter <= 1;
};

var isset = function(obj) {
  if (typeof obj === "undefined" || obj === null) {
    return false;
  } else {
    return true;
  }
};

var isPalindrom = function(str) {
  // reverse original string
  splitString = str.split("");
  reverseArray = splitString.reverse();
  joinArray = reverseArray.join("");

  var checking = checkSpellingOfStr(str);

  if (str == joinArray) {
    strArr = str.split("");
    // console.log("strArr: " + strArr);

    objKeys = makeObjKeys(count, strArr);
    // console.log("filled count before mForN: " + JSON.stringify(count));

    // create array of keys in the count object
    objKeys = Object.keys(count);
    // console.log("objKeys: " + objKeys);

    count = mForN(count, strArr);
    // console.log("count after mForN: " + JSON.stringify(count));

    return mForN_2(count, objKeys);
  } else {
    return 0;
  }
};

var makeObjKeys = function(obj, arr) {
  for (var x = 0; x < arr.length; x++) {
    obj[arr[x]] = null;
  }
  return obj;
};

var checkSpellingOfStr = function(someStr) {
  var formData = {
    someWord: someStr
  };

  $.ajax({
    type: "GET",
    url: url,
    data: formData,
    success: function(result) {
      if (!$.trim(result)) {
      } else {
        console.log(result);
        $("#checkSpelling").html(result);
      }
    }
  });
};

Start everything with the following call:

isPalindrom("mom") ? demoP.innerHTML = "is pal" : demoP.innerHTML = "is not pal";

In my example, I have a form and I listen for a button click as follows:

var palindromeTxt = document.getElementById("palindromeTxt").value;
var btn = document.getElementById("button");
btn.addEventListener("click", function (event) {
  isPalindrom(palindromeTxt) ? demoP.innerHTML = "is pal" : demoP.innerHTML = "is not pal";
});

The following is the php for spell check:

<?php
error_reporting(E_ALL); 
ini_set('display_errors', 1);

if(!empty($_REQUEST['someWord']))
{
    $someWord = $_REQUEST['someWord'];
}

$pspell_link = pspell_new("en");

if (pspell_check($pspell_link, $someWord)) {
  echo trim($someWord) . " is a recognized word in the English language";
} else {
  echo "Your word is either misspelled or that is not a recognized word";
}

You will need pspell installed on your server, as well as adding extension=pspell.so to your php.ini

This is what I did, to get it running locally on my mac:

cd /Users/username/Downloads/php-5.6.2/ext/pspell 

/usr/local/bin/phpize

./configure --with-php-config=/usr/local/php5-5.6.2-20141102-094039/bin/php-config --with-pspell=/opt/local/

make

cp ./modules/* /usr/local/php5-5.6.2-20141102-094039/lib/php/extensions/no-debug-non-zts-20131226

sudo apachectl restart

check your phpinfo file and you should see the following:

pspell
PSpell Support  enabled

Live example

How to check if isset is not set?

It'd fine to use !isset, no issue, but else ifif is completly wrong in your code

Approach will be:-

if(isset($_REQUEST['search'])){  // check that variable is set and have some value or not
    // variable is set and have value
}else {
   // variable is either not set or not have  value
}

if isset statement with javascript?

document.getElementById("element") will return null if the element doesn't exist -- and something not-null if it exists.

Which means you should be able to do something like this :

var areaOption = document.getElementById("element");
if (areaOption) {
    // element exists
} else {
    // element doesn't exist
}

(You could also compare areaOption with null, instead of just checking if it's non-falsy)

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