javascript_basic.md

Answer this questions to check you general understanding of the topic:

Quiz:

1. How do you write a conditional statement for executing some code if i is equal to 5?

   • if (i==5)
   • if i=5
   • if i=5 then
   • if i==5 then

2. What is an array?

   • A set of variables stored in one value
   • A set of several commands
   • A set of values stored in one variable
   • A set of several scripts

3. How to declare a variable?

   • abc = ... and var abc = ...
   • Only abc = ...
   • Only var abc = ...
   • With neither of these

4. What is result of next line of code?

    typeof null
   

   Answer:

   • null
   • object
   • undefined

5. Which of the following function no exist for string?

   • reverse
   • replace
   • substring
   • concat

6. When executed, what value will be alerted to the screen?

    function() {
        var a = 10;
        if (a > 5) {
            a = 7;
        }
        alert(a);
    }
   

   Answer:

   • 7
   • 10
   • null
   • undefined

7. What would be the value alerted by this function?

    function() {
        if (true) {
            var a = 5;
        }
        alert(a);
    }
   

   Answer:

   • 0
   • 5
   • null
   • undefined

8. Assuming I call these functions in order, what value gets alerted?

    var a = 5;
    function first() {
        a = 6;
    }
    function second() {
        alert(a);
    }
   

   Answer:

   • 5
   • 6
   • null
   • undefined

9. There are now two variables with the same name, a. Which one does Javascript pick?

   var a = 5;
   function() {
       var a = 7;
       alert(a);
   }
   

Answer: * 5 * 7

11. When executed, this will pop up three alerts. In order, what are they?

    var a = 6;
    function test() {
        var a = 7;
        function again() {
            var a = 8;
            alert(a);  // First
        }
        again();
        alert(a);  // Second
    }
    test();
    ​alert(a);​  // Third
    

Answer: * 6; 7; 8 * 7; 6; 8 * 8; 7; 6 * 8; 6; 7

12. What's alerted to the screen?

    function getFunc() {
        var a = 7;
        return function(b) {
            alert(a+b);
        }
    }
    var f = getFunc();
    f(5);
    

Answer: * 5 * 7 * 12 * null

13. JavaScript has Math library which can be used like this: Math.max(8,9,10) // result is 10. If I provide an array with certain values then how would you find the max value for that array.

    a = [1,2,3]; //write you code below
    

14. In the following example, what is foo aliased to?

    (function(foo) {
      // What is 'foo' aliased to?
    })(this);
    

Answer: * undefined * global object (window) * null * this

15. What is the result of next line of code?

    "b,ab,sb,".search(/b,/)

Answer: * -1 * 0 * 3 * undefined

16. What will be alerted?

    var f = new Booleand(false); if (f) { alert(f); }

Answer: * nothing * undefined * false * true

Question to all topics:

1. Implement the bubble sort.

2. Why do these yield different results?

    '1' + 2 +  3 ; // Equals '123'
    3  + 2 + '1'; // Equals '51'
    3  + 2 +  1 ; // Equals 6
   

3. Describe how variable hoisting works, and how to avoid bugs that may arise from it.

4. How do these differ?

    function foo() {}
    // versus
    var foo = function() {};
   

5. Explain how to determine if a variable is an array or an object.

6. In one line of code, how you would make a copy of an array?

7. What does this snippet of code do?

    var foo = bar ? bar : 0;
   

8. When might you write something like this, and what is it shorthand for?

    foo && foo.bar();
   

9. How do parseInt and parseFloat differ? When would you use a number's toFixed() method? In what instance might the following code snippet actually make sense to use?

     var my_number = my_string - 0;
   

10. Write a function wich finds all the phone numbers in text (> 10000 chars) and replaces them with the name of the country. If number starts with +380 replace by Ukraine, +7 - Russia, +1 - USA, other - N/A.