how to check typeof var in javascript

Something Like that:
typeof

For that you need to create first html code.

HTML

<p>Type of a var = <span id="demo1"></span></p>
<p>Type of b var = <span id="demo2"></span></p>
<p>Type of c var = <span id="demo3"></span></p>
<p>Type of d var = <span id="demo4"></span></p>
<p>Type of d var = <span id="demo45"></span></p>
<p>Type of e var = <span id="demo5"></span></p>
<p>Instance of e var = <span id="demo6"></span></p>
<p>Type of z var = <span id="demo7"></span></p>
<p>Type of undefined = <span id="demo8"></span></p>
<p>Type of null = <span id="demo9"></span></p>

After that add this JS code.

JS

var a = 3;
document.getElementById('demo1').innerHTML = (typeof a);

var b = "Hello";
document.getElementById('demo2').innerHTML = (typeof b);

var c = {};
document.getElementById('demo3').innerHTML = (typeof c);

var d = [];
document.getElementById('demo4').innerHTML = (typeof d); // Wired!
document.getElementById('demo45').innerHTML = (Object.prototype.toString.call(d)); // better!

function Person(name){
    this.name = name;
}

var e = new Person('Jane');
document.getElementById('demo5').innerHTML = (typeof e);
document.getElementById('demo6').innerHTML = (e instanceof Person);

var z = function(){};
document.getElementById('demo7').innerHTML = (typeof z);

document.getElementById('demo8').innerHTML = (typeof undefined); // make sense
document.getElementById('demo9').innerHTML = (typeof null); // a bug since, like, forever...

[codepen_embed height=”265″ theme_id=”0″ slug_hash=”JyZWGx” default_tab=”result” user=”pradeepanvi”]See the Pen how to check typeof var in javascript by Pradeep Kumar (@pradeepanvi) on CodePen.[/codepen_embed]

Now you can see

Type of a var = number
Type of b var = string
Type of c var = object
Type of d var = object
Type of d var = [object Array]
Type of e var = object
Instance of e var = true
Type of z var = function
Type of undefined = undefined
Type of null = object