- Introducing Conditional Statements 8:39
- Comparison Operators 7:19
- Conditional Statements and Operators Review 7 questions
- Use Comparison Operators 1 objective
- Boolean Values 7:32
- Program Multiple Outcomes 5:45
- Booleans and Else If Review 5 questions
- Write an 'if' Statement 1 objective
- Add an 'else if' Clause 1 objective
- Add a Final 'else' Clause 1 objective
- Test Multiple Conditions With the && Operator 3:57
- Test Multiple Conditions With the || Operator 4:04
- Document Your Code with Comments 4:43
- Multiple Conditions and JavaScript Comments Review 6 questions
- The Conditional Challenge 2:17
- The Conditional Challenge Solution 6:23
- Use Multiple Conditions 1 objective
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Comparison Operators
7:19The most important part of a conditional statement is the condition itself. It's a test that checks to see if something is either true or false. JavaScript provides "comparison operators" to help with conditional statements.
In the previous video, you learned
about an important programming concept,
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the conditional statement.
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You used the conditional statement
to control the flow of a program.
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It made decisions and carried out actions
accordingly depending on different inputs.
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The most important part of the conditional
statement is the condition itself.
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It's a test that checks to see if
something is either true or false.
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For example, in this code, the condition
is spaceShips === 0, which breaks down
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to a simple question, is the value stored
in the variable spaceShips equal to zero?
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The answer is either yes or no.
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If the answer is yes, the game is over and
an alert dialog appears.
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As it turns out, all conditions no matter
how complex, end up with a simple yes or
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no answer, or as computers like
to think of it, true or false.
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JavaScript provides lots
of ways to test things.
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We've seen the triple equals operator,
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which is a way to test
the equality of two things.
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You can use that operator to see if the
value a user typed matches a particular
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string or if the value in
a variable is a particular number.
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JavaScript provides other
comparison operators to help with
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conditional statements.
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Some of them you might
already know from math.
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For example, the greater than and
less than symbols are often used for
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comparing numeric values.
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For instance,
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you can make a game harder if
the player's score is greater than 1000.
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Or on the other hand,
if a visitor is less then a certain age,
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you can tell them to come
back when they are older.
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To get some practice understanding
conditions, let's look at a few examples.
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In the JavaScript console, I'll start by
typing a few conditions greater than and
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less then operators and you try to
decide if a condition is true or false.
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First, 3 is greater than 2, this is true,
because 3 is a larger number than 2.
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Next, 100 is greater than 100,
this is false,
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because the two values are the same,
100 isn't greater than itself.
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How about 100 is greater than or
equal to 100?
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Well, this is true, because although
the value on the left isn't
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greater than the value on the right,
it's still equal to it.
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Here's another one,
negative 12 is less than 0.
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And this is true because negative numbers
are smaller than positive numbers or zero.
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Okay, one more, the string apple
is less than the string bear.
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The greater than and less than operators
aren't limited to just numbers.
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In this case, the comparison is true
because the first letter of the string on
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the left, the a in apple, comes before
the first letter of the second string,
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the b in bear,
that is a comes before b in the alphabet.
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Also in comparison checks, letter strings
always come after number strings.
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For instance, if you check if
a number string like 100 is
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less than a letter string like Apple,
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a number is less than any letter,
so this returns true.
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JavaScript provides two ways
to test if values are equal,
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the double equal sign and
the triple equal sign.
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The double equal sign is
called the equality operator.
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It lets you test if two
values are the same, but
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makes some allowances for
different types of values.
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For example, 3 inside quotes is a string,
and 3 without quotes, it's a number.
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But if you use the double equal sign,
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then the browser converts the string
to a number before comparing them.
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And this returns true,
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because the JavaScript engine
converts the string to the number 3,
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and says that yes, the number 3 is
the same as the second number 3.
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The triple equal sign is called
a strict equality operator,
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it compares the type as well as the value.
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For example,
a strict comparison like this is false,
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because one value is a string and
the other is a number.
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They are not the same type of value,
so they are not equal.
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It might seem like using the double
equals operator is better since it's more
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flexible.
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However, JavaScript developers tend
to use the triple equals operator and
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avoid the double equals, why?
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Well, you can get into some weird
situations using the double equals
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operator.
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Here's one example,
an empty string is equal to 0.
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This returns true, an empty string
is equal 0, strange isn't it?
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And you can learn why this happens in
the teacher's notes with this video.
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But notice, that if you use a strict
equality operator, the result is false.
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In many cases, the two equality
operators work the same, but
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there are a few cases,
like the one I just showed you,
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where the double equal sign
might get you in trouble.
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So for that reason, I'll use strict
equality or the triple equals operator for
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the rest of this course.
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All right, now,
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let's look at a few examples using
the strict equality operator.
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165 === 165.9, this is false,
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because the two numbers are not equal.
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How about the ' Python ' === the " HTML '?
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This is also false because those
strings have different letters in them.
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Whereas ' JavaScript ' ===
' JavaScript ' is true,
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because those strings
are exactly the same.
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But remember that JavaScript
is case sensitive.
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So comparing Javascript in all lowercase,
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with JavaScript as it's
normally written is false,
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because the first string has all lowercase
letters, and the second does not.
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A lowercase j isn't
equal to an uppercase J.
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JavaScript also provides ways to test
whether two values are not equal.
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There's the not equal or
inequality operator.
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It's an exclamation mark
followed by an equal sign.
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The exclamation point is called a logical
NOT operator, so != means not equal to.
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But keep in mind that it's better to use
the strict inequality operator with two
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equal signs, for
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the same reasons, it's better to use
the strict equality comparison operator.
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So let's look at a few examples of
the strict inequality operator.
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First, 10 !== 9,
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this is true because 10 is not equal to 9.
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How about ' 10 ' !== 10?
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This is also true because the value
on the left is a string, and
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the value on the right is a number,
so the two types do not match.
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Let's check if 'Java' !==
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'java' in all lowercase.
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And this is true,
because the uppercase J in the first
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string isn't the same as
the lowercase j in the second string.
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Finally, negative 59 !== negative 59,
well,
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this is false,
because the two numbers are the same.
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