JavaScript Conditional Statements

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Week 12:
JavaScript
Conditional Statement
Subject Code: COMP121
By: Marlon Jamera
Email: mbjamera@ama.edu.ph

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JavaScript
Conditional Statement

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Scope of the Lesson
• Conditional Statements
• The if statement
• The else statement
• The switch statement
• The break Keyword
• Different Kind of Loops
• JavaScript for loop
• JavaScript for/in loop
• JavaScript while loop
• JavaScript do/while loop

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Learning Outcomes
By the end of the lesson, you will be
familiar and know how the website works
using JavaScripts.
• Discuss the introduction to JavaScript
and using conditional statements.
• Understand the coding syntax using the
break keywords.
• Explain thoroughly the coding styles of
different kinds of loops.

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Conditional Statements
• Conditional statements are used to
perform different actions based on
different conditions.
• Very often when we write code, we
wanted to perform different actions for
different decisions.
• We can use conditional statements in our
code to do this.

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Conditional Statements
• In JavaScript, we have the following
conditional statements:
• Use if to specify a block of code to be
executed, if a specified condition is true
• Use else to specify a block of code to
be executed, if the same condition is
false.
• Use else if to specify a new condition
to test, if the first condition is false.
• Use switch to specify many alternative
blocks of code to be executed.

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The IF Statement
• Use if to specify a block of code to be
executed, if a specified condition is true.
• Syntax:
if (condition) {
block of code to be executed if
the condition is true
}
• Note that if is in lower case. Uppercase
letters will generate a JavaScript error.

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The IF Statement
• Example:
• Make a "Good day" greeting if the hour
is less than 18:00:
if (hour < 18) {
greeting = "Good day";
}
• The result of greeting will be:
• Good day

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The ELSE Statement
• Use else to specify a block of code to be
executed, if the same condition is false.
if (condition) {
the condition is true
} else {
the condition is false
}

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The ELSE Statement
• Example:
• If the hour is less than 18, create a "Good
day" greeting, otherwise "Good evening":
if (hour < 18) {
} else {
greeting = "Good evening";
}
• The result of greeting will be:
• Good day

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The ELSE IF Statement
• Use else if to specify a new condition to
test, if the first condition is false.
if (condition1) {
condition1 is true
} else if (condition2) {
the condition1 is false and condition2
is true
} else {
the condition1 is false and condition2
is false
}

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The ELSE IF Statement
• Example:
• If time is less than 10:00, create a "Good
morning" greeting, if not, but time is less
than 20:00, create a "Good day" greeting,
otherwise a "Good evening":
if (time < 10) {
greeting = "Good morning";
} else if (time < 20) {
} else {
greeting = "Good evening";
}

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The SWITCH Statement
• Use switch to specify many alternative
blocks of code to be executed.
• Syntax:
switch(expression) {
case n:
code block
break;
case n:
code block
break;
default:
default code block
}

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• How switch works?
• The switch expression is evaluated
once.
• The value of the expression is
compared with the value of each case.
• If there is a match, the associated
block of code is executed.

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• Example:
• The getDay() method returns the
weekday as a number between 0 and 6.
(Sunday=0, Monday=1, Tuesday=2 ..)
• Use the weekday number to calculate
weekday name.

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The Break Keyword
• When the JavaScript code interpreter
reaches a break keyword, it breaks out of
the switch block.
• This will stop the execution of more
code and case testing inside the block.
• Note: When a match is found, and the
job is done, it is time for a break. There is
no need for more testing.

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Different Kinds of Loops
• JavaScript supports different kinds of
loops:
• for – loops through a block of code a
number of times.
• for/in – loops through the properties
of an object.
• while – loops through a block of code
while a specified condition is true.
• do/while - also loops through a block
of code while specified condition is
true.

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JavaScript FOR LOOP
• Loops can execute a block of code a
number of times.
• Loops are handy, if you want to run the
same code over and over again, each time
with a different value. Often this is the
case when working with arrays:
text += cars[0] + "<br>";

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JavaScript FOR LOOP
• The for loop is often the tool you will
use when you want to create a loop.
• The for loop has the following syntax:
for (statement 1; statement
2; statement 3) {
code block to be executed
}

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JavaScript FOR LOOP
•Often this is the case when working with
arrays:
• We can write:
for (i = 0; i < cars.length; i++) {
text += cars[i] + "<br>";

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JavaScript FOR LOOP
• Statement1 is executed before the loop
(the code block) starts.
• Statement2 defines the condition running
the loop (the code block)
• Statement3 is executed each time after
the loop (the code block) has been
executed.
• Example:
for (i = 0; i < 5; i++) {
text += "The number is " + i
+ "<br>";
}

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JavaScript FOR/IN LOOP
• The JavaScript for/in statement loops
through the properties of an object:
var person = {fname:"John",
lname:"Doe", age:25};
var text = "";
var x;
for (x in person) {
text += person[x];
}

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JavaScript WHILE LOOP
• The while loop loops through a block of
code as long as a specified condition is
true.
• Syntax:
while (condition) {
}

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JavaScript WHILE LOOP
• Example:
• The code in the loop will run over and
over again, as long as variable (i) is less
than 10.
while (i < 10) {
text += "The number is " + i;
i++;
}

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JavaScript DO/WHILE LOOP
• The do/while loop is a variant of the
while loop. This loop will execute the
code block once, before checking if the
condition is true, then it will repeat the
loop as long as the condition is true.
• Syntax:
do {
}
while (condition);

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JavaScript DO/WHILE LOOP
• Example:
• The loop will always be executed at least
once, even if the condition is false,
because the code block is executed before
the condition is tested:
do {
text += "The number is " + i;
i++;
}
while (i < 10);

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Let’s call it a day,
Thank you!

JavaScript Conditional Statements

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