Assignment Operators
Assignment operator assigns value to a variable based on the evaluated value of a specified expression. The basic symbol used for assignment operator is an equal sign(=). For example, x = 10 assigns 10 to variable x.

You can use also shorthand assignment operator, like the following:

 

The basic computational operators are addition(+), substraction(-), multiplication(*) and division(/). These operators take the numerical quantities of the operands and perform the operation that evaluates to a single numerical value. Remember that in addition if one of the operands is a string value, string concatenation is performed rather than adding their numerical values.

Other computational operators used in JavaScript are modulus(%), increment(++) and decrement(--).

Logical Operators
Logical operators are used to carry out some conditional test. The following are the logical operators used in JavaScript:

The comparison operators(<, <=, > and >=) can be used in both numeric and string type. If comparing the numbers, they perform comparisons on the numerical quantities of the operands. If the operands are of string type, they perform comparisons according to dictionary order. For example, "click" < "press" returns true.

Boolean logical operators are used to compare Boolean values and return Boolean value. The Boolean logical operators are logical AND(&&), logical OR(||) and logical NOT(!). The table below shows the returned value of the Boolean logical operators based on the Boolean values of the operands:
 

Expression exp1 exp2 Returned Value
exp1 && exp2 true true true
exp1 && exp2 false true false
exp1 && exp2 true false false
exp1 && exp2 false false false
exp1 || exp2 true true true
exp1 || exp2 false true true
exp1 || exp2 true false true
exp1 || exp2 false false false
!exp1 false   true
!exp1 true   false

Computational Operators

Symbols Description
+ Addition, String concatenation
- Subtraction, Unary negation
* Multiplication
/ Division
++ Pre-increment, Post-increment
-- Pre-decrement, Post-decrement

 

Pre-increment and Post-increment
JavaScript uses a unary operator ++ that adds one(1) to operand. There are two ways you can use the increment operator; pre-icrement and post-increment.

If this operator is placed before the operand like ++x, it's called pre-increment operator. It returns the value of x after adding 1 to it. For example, the initial value of x is 4, ++x sets x to 5 and returns 5.

If this operator is placed after the operand like x++, it's called post-increment opearator. It returns the value of x before adding 1 to it. For example, the initial value of x is 4, x++ sets x to 5 and returns 4.

 


Conditions

Conditions are logical expressions that use comparison and logical operators and evaluate to a Boolean value of true or false

Common comparison used in this course:

Simple conditions use comparison operators to compare numbers and strings and numerical and string expressions.

  • Compound Conditions use logical operators to combine logical conditions.

       

    • Common logical operators used in this course:

       

 


 

  if-else

The if-else statement is one way of testing conditions in your program. Below you'll see the format for using if-else. If condition A is true, statementsA will be performed. Then, program flow will jump over all other else conditions and execute statementsD. If conditionA is false, conditionB will be tested. If true, statementsB will be performed, after which statementsD will be performed. If both conditionA and conditionB fail, statementsC will be performed, then statementsD. You can have multiple else if conditions or can omit both the else ifs and the else altogether.

 

if (condition1)
 {
       statementsA;  (one or more statements)
 }
else if (condition2)
 {
       statementsB;  (one or more statements)
 }
else
 {
       statementsC;  (one or more statements)
 }

statementsD;

Below you'll see an example of an if-else statement. Try changing the value of the divisor to see how the program behaves differently when it equals 0 or not.

 

<script language="JavaScript">
  <!-- Hide JavaScript code from old browsers
      var divisor = 10;
      var number = 100;
      var answer;

      // test the value of the divisor
      if (divisor == 0)
       {
         document.writeln("error. divisor equal to 0");
       }
      else
       {
         answer = number/divisor;
         document.writeln(answer);
       }  
      document.writeln("<br>" + "The divisor is " + divisor); 
  // end hiding code -->
</script>