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Javascript - Conditional Statement

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• Javascript - Conditional Statement
  • Conditional Statement
  • if Statement
  • else Statement
  • else if Statement
  • switch Statement
    • The break Keyword
    • The default Keyword
    • Shared Block

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Conditional Statement

• Conditional Statement
  • used to perform different actions based on different conditions.

Situation to execute	Statement
condition is true	if
condition is false	else
new condition	else if
alternative conditiona	switch

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if Statement

• Use the if statement to specify a block of JavaScript code to be executed if a condition is true.

• Syntax

if (condition) {
  //  block of code to be executed if the condition is true
}

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else Statement

• Use the else statement to specify a block of code to be executed if the condition is false.

if (condition) {
  //  block of code to be executed if the condition is true
} else {
  //  block of code to be executed if the condition is false
}

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else if Statement

• Use the else if statement to specify a new condition if the first condition is false.

• Syntax

if (condition1) {
  //  block of code to be executed if condition1 is true
} else if (condition2) {
  //  block of code to be executed if the condition1 is false and condition2 is true
} else {
  //  block of code to be executed if the condition1 is false and condition2 is false
}

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switch Statement

• Use the switch statement to select one of many code blocks to be executed.

• The switch expression is evaluated once. The value of the expression is compared with the values of each case.

  • If there is a match, the associated block of code is executed.
  • If there is no match, the default code block is executed.

• If multiple cases matches a case value, the first case is selected.

• If no matching cases are found, the program continues to the default label.

• If no default label is found, the program continues to the statement(s) after the switch.

• Strict Comparison

  • Switch cases use strict comparison (===).

  • The values must be of the same type to match.

  • A strict comparison can only be true if the operands are of the same type.

• Syntax:

switch (expression) {
  case value1:
    // code block
    break;
  case value2:
    // code block
    break;
  default:
  // code block
}

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The break Keyword

• When JavaScript reaches a break keyword, it breaks out of the switch block. This will stop the execution inside the switch block.

• It is not necessary to break the last case in a switch block. The block breaks (ends) there anyway.

• Note: If you omit the break statement, the next case will be executed even if the evaluation does not match the case.

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The default Keyword

• The default keyword specifies the code to run if there is no case match.

• The default case does not have to be the last case in a switch block.

  • If default is not the last case in the switch block, remember to end the default case with a break.

console.log("\n-------- switch --------\n");
switch (new Date().getDay()) {
  default:
    console.log("Weekday");
    break;
  case 6:
    console.log("Saturday");
    break;
  case 0:
    console.log("Sunday");
}

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Shared Block

• When multiple cases share a code block.

console.log("\n-------- switch --------\n");
switch (new Date().getDay()) {
  case 4:
  case 5:
    console.log("Soon it is Weekend");
    break;
  case 0:
  case 6:
    console.log("It is Weekend");
    break;
  default:
    console.log("Looking forward to the Weekend");
}

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