1if (typeof myVar === 'string' || myVar instanceof String)
2// it's a string
3else
4// it's something else
5

1console.log(typeof "how are you?")
2"string"
3console.log(typeof false) / console.log(typeof true)
4"boolean"
5console.log(typeof 100)
6"number"

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

1typeof("string"); //string
2typeof(123); //number

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}

1console.log(typeof 93);
2// Output = "number"
3
4console.log(typeof 'Maximum');
5// Output = 'string'
6
7console.log(typeof false);
8// Output = "boolean"
9
10console.log(typeof anUndeclaredVariable);
11// Output = "undefined"