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JavaScript JavaScript Basics (Retired) Making Decisions with Conditional Statements Boolean Values

Aaron Coursolle
Aaron Coursolle
18,014 Points
Posted by Aaron Coursolle
Aaron Coursolle
18,014 Points

I was following along until shorthand was introduced

This is a code that contains two conditional statements, but I'm only showing the second one below:

if (correctGuess === true) {
  document.write('<p>You guessed the number!</p>');
} else {
  document.write('<p>Sorry.  The number was ' + randomNumber + '</p>');
}

This code makes sense to me, but in the shorthand:

if (correctGuess) {
  document.write('<p>You guessed the number!</p>');
} else {
  document.write('<p>Sorry.  The number was ' + randomNumber + '</p>');
}

the code does not. How does it work if you aren't explicitly stating if correctGuess is true or false.

2 Answers

Geoff Parsons
Geoff Parsons
11,679 Points

Whatever is inside of the parenthesis of the conditional is evaluated to true or false and that determines if that particular block of code is run. For instance you could ask if a variable has the value "tacos"

if ( food === "tacos" ) {
// do something
}

Which will evaluate food === "tacos" to either true or false. If the variable you are checking already contains one of the literal values true or false then you do not need to use an equality operator (===).

  var myBoolean = true;
  if ( myBoolean ) {
    // code here will run
  }

  var otherBoolean = false;
  if ( otherBoolean ) {
    // code here will not run
  }
Nick Hettinger
Nick Hettinger
10,815 Points

I don't understand how the program would know which code to run if the correctGuess variable can be either true or false (dependent on user input). For example, if the user guesses wrong, then the correctGuess value would stay false. In this case, what prevents the program from running the code that tells the user that their guess was correct?

Manuel Sanchez
Manuel Sanchez
8,971 Points
Manuel Sanchez
Manuel Sanchez
8,971 Points

Nick, that's why you set the variable correctGuess to false, so its value can only be set to true when the user guess is right. In other words, you're assuming that the user is wrong until its input proves the opposite. Making "hypotheses" beforehand is a common programming pattern. You'll see a lot of programming problems that can be solved by this "it's true until proven false" (and vice versa, but not that frequently) approach.

Victoria Felice
Victoria Felice
14,760 Points
Victoria Felice
Victoria Felice
14,760 Points

Hi Aaron, I think that you got the main point. This is just a shorthand.

"if (correctGuess)" means "if (correctGuess === true)". In other words:

Longhand:

if (correctGuess === true)

Shorthand:

if (correctGuess)

I found a good article about JavaScript shorthands http://www.sitepoint.com/shorthand-javascript-techniques/ This particular case is mentioned there as well: paragraph 8. If Presence Shorthand. HTH.

Aaron Coursolle
Aaron Coursolle
18,014 Points
Aaron Coursolle
Aaron Coursolle
18,014 Points

Looks like a very helpful article. Thank you.