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

1> typeof "foo"
2"string"
3> typeof true
4"boolean"
5> typeof 42
6"number"
7
8if(typeof bar === 'number') {
9   //whatever
10}

1//typeof() will return the type of value in its parameters.
2//some examples of types: undefined, NaN, number, string, object, array
3
4//example of a practical usage
5if (typeof(value) !== "undefined") {//also, make sure that the type name is a string
6  	//execute code
7}

1typeof operando