Test Response

Test 1’s answer is below, you can download test 2’s answer in GitHub or view it here http://23.105.194.63/

1. How to verify if a variable is an array?

What I know is this one

Array.isArray(variable);

But after a short search, I found a much better and faster way to do it

variable.constructor === Array

and it seems to be the fastest way that runs on Chrome.

2. What is a ternary operator? Give an example

Ternary operator is an operator uses three operands. Most often used one is

[condition]?[expression1]:[expression2]

which is a short and clean for if statement.

Basically the logic is

if([condition]){
	[expression1]
}else{
	[expression2]
}

3. What are the differences between null and undefined?

Difference:

null: The value of the variable is defined to be null

var a = null; //the value of a is null

undefined: The variable is not defined, there should be a value

var a; //the value of a is not defined

and

undefined === null //false

Same:

if (!undefined) console.log('undefined is false');
// undefined is false

if (!null) console.log('null is false');
// null is false

undefined == null
// true

4. What is the output ?

   var num = 10,
   	 name = "Addy Osmani",
     obj1 = {
   	value: "first value"
     },
     obj2 = {
      value: "second value"
     },
     obj3 = obj2;
   function change(num, name, obj1, obj2) {
     num = num * 10;
     name = "Paul Irish";
     obj1 = obj2;
     obj2.value = "new value";
   }
   change(num, name, obj1, obj2);
   console.log(num);
   console.log(name);
   console.log(obj1.value);
   console.log(obj2.value);
   console.log(obj3.value);

the output should be

10
Paul Irish
first value
new value
new value

The global value will not be affected, but the property of an object could be affected in a function porcedure.

5. What is the console output ?

   for(var i=0;i<10;i++){
     setTimeout(function(){
         console.log(i);
     }, 200);
   }

the output is (10 '10's)

because the for loop has already finished even before the timeout, and variable i become 10. Then the console.log(i) are all executed after timeout. so the result are 10 '10's

6. What is the output ?

var Person = function(name){
       this.myname = name;
};
Person.prototype.hello = function(){
       return "Hello I'm "+this.myname+" !";
}
var a = new Person("Frank");
function talk(fn){
       console.log(fn());
}
talk(a.hello);

After some debugging, the output is still Hello I'm undefined ! and I tried to log out the constructor of Person, the output is:

function Function() {
    [native code]
}

But I think the correct output should be Hello I'm Frank !