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

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

1if (typeof i != "number") {
2    console.log('This is not number');
3}

1> typeof "foo"
2"string"
3> typeof true
4"boolean"
5> typeof 42
6"number"