Exercise 12.1

This is Exercise 12.1, lecture on Javascript quirks, used in the course IDATA2301 Web technologies at NTNU, campus Aalesund.

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Purpose

The purpose of the exercise is practice understanding variable scope and creating variables in the scope you want them to be.

Instructions

  1. Create a new HTML document. Include a file named app.js. In this exercise you will be placing all the Javascript code in app.js.
  2. Create a global variable named g, set value g=3.
  3. Create a function printG. Inside it print a message "The value of g is " + g (by print we mean console.log in this exercise).
  4. Invoke the function printG after you have set value for g. (invoke the function means "call the function, execute it").
  5. Invoke the function printG one more time. But this time put the invocation (function call) on the first line of app.js file.
  6. Take a moment to think - why do you get the results you get? Hint: remember hoisting and execution!
  7. Create two functions: a and b. Leave their body empty for now.
  8. Invoke function a from the global context.
  9. Invoke function b from the global context.
  10. Create variable x=12 - it must be available in both functions a and b as well as the global context. To test if it works: print the value of x in function a, function b and globally.
  11. Print window.x in the console. Did you see 12?
  12. Create a variable y=15. Choose the right place (lexical environment) for the variable: it should be available only inside function a and nowhere else. Test if it works correctly: printing it should work from function a, but should fail from function b and also from the global context.
  13. Create a new function c and have a variable z=667 in such a way that z is available inside functions b and c, but nowhere else. Hints:
    • Think about outer environments!
    • Where should you place function c?

Solution

You can find a solution here.