check data type in javascript

typeof("string"); //string
typeof(123); //number

function doSomething(x) {
  if(typeof(x) === 'string') {
    alert('x is a string')
  } else if(typeof(x) === 'number') {
    alert('x is a number')
  }
}

> typeof "foo"
"string"
> typeof true
"boolean"
> typeof 42
"number"

if(typeof bar === 'number') {
   //whatever
}

//typeof() will return the type of value in it's parameters.
//some examples of types: undefined, NaN, number, string, object, array

//example of a practical usage
if (typeof(value) !== "undefined") {//asuming value is already set
  	//execute code
}

typeof("iAmAString");//This should return 'string'
//NO camelCase, as it is a JS Keyword

console.log(typeof 93);
// Output = "number"

console.log(typeof 'Maximum');
// Output = 'string'

console.log(typeof false);
// Output = "boolean"

console.log(typeof anUndeclaredVariable);
// Output = "undefined"

> typeof "foo"
"string"
> typeof true
"boolean"
> typeof 42
"number"

// You can use the built-in method 'typeof' in order to check the variable datatype

//examples:

typeof "hello" // "string"

//or
var a = 1;
typeof(a);
//the output will be > 'number'

console.log(typeof 42);

console.log(typeof 'blubber');

var x = "Hello World";
typeof x; // "string"