JavaScript operators and Control statements

An operator

1. Basic Concepts

Expression: A phrase made up of constants/variables and operators

Operands: Constants and variables in an expression become operands

Monocular operator: becomes a single-mesh operator with only one operand

Multi-mesh Operator: Become a multi-mesh operator with multiple operands

2 "+" for strings

Concatenate multiple strings together

3 Assignment operators

• =: x=y
• + = X+=y X=x+y
• -= X-=y x=x-y
• *= x*=y X=x*y
• /= x/=y x=x/y
• %= x%=y x=x%y

4 Arithmetic operators

• Subtraction: +-*/
• Modulo operator:%
• Plus and minus operators: +-
• Increment decrement Operator: + +--: Make number increment/decrement 1 (note the difference between front and rear)
• If there is no assignment front and back, the same.
• If there is an assignment: the pre-increment/decrement assignment is calculated first, the reverse is reversed

5 comparison operators

The comparison operator returns a Boolean value

• Equality operator = =: Different data types are automatically converted to equal data types and then compared
• equals operator = = = Congruent (value and type)
• Unequal operator!==:
• ! = does not equal
• > Greater than
• < less than
• >= greater than or equal to
• <= less than or equal to

6 logical Operators

• Logical operators are used to determine the logic between variables or values.
• && and----Both are true
• || or (OR)----L at least one is true, both are false, only false
• ! Not (non)

7 Conditional operators

• Execute one of the two statements according to the criteria, using the symbol? : The syntax is as follows:
  Conditional expression? Statement 1: Statement 2
• Parameter description:
• conditional expression, the result is treated as a Boolean value
• Statement 1: Executes if the conditional expression returns true
• Statement 2: Executes if the conditional expression returns false

Two control statements

1.if Selection Statement

• if () statement-Use this statement to execute code only if the specified condition is true
• if (). Else statement-executes code when the condition is true and executes additional code when the condition is false
• if () ... else if () ... else statement-Use this statement to select one of several code blocks to execute an expression in the
• if statement () automatically converted to a Boolean value.

var a=5;   var b=4;   if (a>b) {      alert ("A is the best")  }Elseif(a==b) {      alert ( "We are as good"  )}else{      alert ("B is the best")  }  </ Script>
Result  A is the best.

2.SWITCH Branch Structure

Use the switch statement to select one of several code blocks to execute.

Grammar:
Switch (n)
{
Case 1:
Executing code block 1
Break
Case 2:
Executing code block 2
Break
Default
N code that executes when it differs from Case 1 and 2
}

<script>varDay= "Sunday"Switch(day) { Case"Sunday": Alert ("Today it ' s Sunday");  Break;  Case"Monday": Alert ("Today it ' s Monday");  Break;  Case"Tuesday": Alert ("Today it ' s Tuesday");  Break;  Case"Wednesday:": Alert ("Today it ' s Wednesday");  Break;  Case"Thursday": Alert ("Today it ' s Thursday");  Break;  Case"Friday": Alert ("Today it ' s Friday");  Break;  Case"Saturday": Alert ("Today it ' s Saturday");  Break; default: Alert ("Illegal characters"); }    </script>
ResultsToday it ' s Sunday

3 for Loop statement

Grammar:
for (statement 1; Statement 2; Statement 3)
{
code block to be executed
}

• Statement 1 executes before the Loop (code block) starts
• Statement 2 defines a condition that runs a loop (code block), and if statement 2 returns True, the loop starts again, and if False is returned, the loop ends.
• Statement 3 executes after a loop (code block) has been executed
• Statement 1 is optional, that is, you do not use statement 1.
• If you omit statement 2, you must provide a break within the loop;

For loop implementation 99 multiplication table  
  <script> for        (i=1;i<=9;i++) {            for (j=1;j<=i;j++) {                   document.write (J+ ' x ' +i+ "=" +i*j+ "&nbsp&nbsp&nbsp")             }             document.write (' < Br> ')        }    </script>

JavaScript operators and Control statements