The function presented below can be used to get the type of a JavaScript variable, and also, to check if a variable is of a certain type.
Here's the function:

function checkType(obj, type) {
  // coursesweb.net/
  // if type not specified (null), returns a string with the object (obj) type
  if(type == null) return obj.constructor.toString().split(' ')[1].replace(/\(\)/g,'').toLowerCase();
  else {
    //returns true if is it is type, else, false
    if (obj.constructor.toString().match(new RegExp(type, 'i', 'g'))) return true;
    else return false;
  }
}
The function has two parameters: "obj", for the variable (or object) you want to check, and "type", which is a string with the name of the type to test.
If the type of "obj" is the name specified in the "type" parameter, the function returns True, otherwise, returns False.
If no argument specified for "type", the function returns a string with the type of "obj".

Here's some examples.

Get variable type

- To get the "obj" type, the second argument ("type") no need to be specified.
<script type="text/javascript"><!--
// function to check /get obj type
function checkType(obj, type) {
  // if type not specified (null), returns a string with the object (obj) type
  if(type == null) return obj.constructor.toString().split(' ')[1].replace(/\(\)/g,'').toLowerCase();
  else {
    // returns true if is it is type, else, false
    if (obj.constructor.toString().match(new RegExp(type, 'i', 'g'))) return true;
    else return false;
  }
}

var str = 'a string';
var num = 78.5;
var arr = new Array();
var obj = new Object();
var json_array = [7, 8, 'abc'];
var json_object = {'ab': 'xyz', 'arr': [1, 2]};

// display alert with the type of each variable created above
alert( checkType(str) );               // string
alert( checkType(num) );               // number
alert( checkType(arr) );               // array
alert( checkType(obj) );               // object
alert( checkType(json_array) );        // array
alert( checkType(json_object) );       // object
--></script>

- The function returns the type of 'obj' in lowercase string, so, to check the type of a variable, just add for "type" argument a string with the name of type you want to check.

Check variable type

<script type="text/javascript"><!--
// function to check /get obj type
function checkType(obj, type) {
  // if type not specified (null), returns a string with the object (obj) type
  if(type == null) return obj.constructor.toString().split(' ')[1].replace(/\(\)/g,'').toLowerCase();
  else {
    // returns true if is it is type, else, false
    if (obj.constructor.toString().match(new RegExp(type, 'i', 'g'))) return true;
    else return false;
  }
}

var str = 'a string';
var num = 78.5;
var arr = new Array();
var obj = new Object();
var json_array = [7, 8, 'abc'];
var json_object = {'ab': 'xyz', 'arr': [1, 2]};

// display alert with true, or false
alert( checkType(str, 'string') );               // true
alert( checkType(num, 'number') );               // true
alert( checkType(arr, 'array') );                // true
alert( checkType(obj, 'object') );               // true
alert( checkType(json_array, 'array') );         // true
alert( checkType(json_object, 'array') );        // false
--></script>

Another example, if a variable, "arr" is Array, alert its first element.
<script type="text/javascript"><!--
// function to check /get obj type
function checkType(obj, type) {
  // coursesweb.net/
  // if type not specified (null), returns a string with the object (obj) type
  if(type == null) return obj.constructor.toString().split(' ')[1].replace(/\(\)/g,'').toLowerCase();
  else {
    // returns true if is it is type, else, false
    if (obj.constructor.toString().match(new RegExp(type, 'i', 'g'))) return true;
    else return false;
  }
}

var arr = ['coursesweb.net', 'javascript', 'course'];

// if "arr" is Array, alert its first element
if(checkType(arr, 'array')) {
  alert(arr[0]);
}
--></script>

Daily Test with Code Example

HTML
CSS
JavaScript
PHP-MySQL
Which tag is used in <table> to create table header cell?
<thead> <th> <td>
<table><tr>
  <th>Title 1</th>
  <th>Title 2</th>
</tr></table>
Which CSS property sets the distance between lines?
line-height word-spacing margin
.some_class {
  line-height: 150%;
}
Which function opens a new browser window.
alert() confirm() open()
document.getElementById("id_button").onclick = function(){
  window.open("http://coursesweb.net/");
}
Indicate the PHP function that returns an array with names of the files and folders inside a directory.
mkdir() scandir() readdir()
$ar_dir = scandir("dir_name");
var_export($ar_dir);
Get and Check variable type in JavaScript

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