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Conditional Statements

There comes a time within a program, where we need to do something based on operand comparison, for this we use conditional statements. In this lesson we look at the if....else construct for basic conditional handling. All premutations of the if....else construct just use one of the comparison operators available in Javascript to test one operand against another.

All the comparison operators are discussed in detail in JavaScript Reference - Comparison Operators so we won't go into them here.

There are various forms of the if....else construct which we will cover as we go through this lesson.

Simple if Statement


The basic if statement compares the operands and returns boolean true or false.

If the boolean is true the statement(s) are executed.




var aVariable = 1, bVariable = 1;

// Compare some operands.
if (aVariable == bVariable) {
  alert('true');
}


Press the button below to action the above code:



Single if....else Construct


The single if....else construct compares the operands and returns boolean true or false.

If the boolean is true the statement(s) following the if are executed.

If the boolean is false the statement(s) following the else are executed.




var aVariable = 1, bVariable = 2;

// Compare some operands.
if (aVariable == bVariable) {
  alert('true');
} else {
  alert('false');
}


Press the button below to action the above code:



Multiple if Construct


The multiple if construct compares the operands and returns boolean true or false for each statement.

If the boolean is true the statement(s) following the if or else....if are executed.

If the boolean returned is false the next else....if statement(s) is checked and so on.

If none of the else....if statements returns true the final else statement(s) will be false and so any statement(s) after this will be executed.




var aVariable = 4, bVariable = 2, cVariable = 3, dVariable = 4;

// Compare some operands.
if (aVariable == bVariable) {
  alert('statement 1 executed');
} else if (aVariable == cVariable) {
  alert('statement 2 executed');
} else if (aVariable == dVariable) {
  alert('statement 3 executed');
} else {
  alert('statement 4 executed');
}


Press the button below to action the above code:



Lesson 3 Complete

In this lesson we looked at the if....else construct and the various ways we can make use of it.


Related Tutorials

JavaScript Advanced Tutorials - Lesson 1 - Advanced Conditional Statements


What's Next?

In the next lesson we take our first look at JS loops with the while and do....while loops.


Reference

JavaScript Reference - if....else construct
JavaScript Reference - comparison operators



  

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