1var foo = "Hello";
2console.log(typeof foo); // string

1function doSomething(x) {
2  if(typeof(x) === 'string') {
3    alert('x is a string')
4  } else if(typeof(x) === 'number') {
5    alert('x is a number')
6  }
7}

1// get type of variable
2
3var number = 1
4var string = 'hello world'
5var dict = {a: 1, b: 2, c: 3}
6
7console.log(typeof number) // number
8console.log(typeof string) // string
9console.log(typeof dict)   // object

1typeof operando

1// You can use the built-in method 'typeof' in order to check the variable datatype
2
3//examples:
4
5typeof "hello" // "string"
6
7//or
8var a = 1;
9typeof(a);
10//the output will be > 'number'

1var x = 12345; 
2console.log(typeof x) // number
3x = 'string'; 
4console.log(typeof x) // string
5x = { key: 'value' };
6console.log(typeof x) // object