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The 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.
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In the previous video, you learned
about an important programming concept,
0:00
the conditional statement.
0:04
You used the conditional statement
to control the flow of a program.
0:05
It made decisions and carried out actions
accordingly depending on different inputs.
0:08
The most important part of the conditional
statement is the condition itself.
0:14
It's a test that checks to see if
something is either true or false.
0:18
For example, in this code, the condition
is spaceShips === 0, which breaks down
0:22
to a simple question, is the value stored
in the variable spaceShips equal to zero?
0:27
The answer is either yes or no.
0:32
If the answer is yes, the game is over and
an alert dialog appears.
0:35
As it turns out, all conditions no matter
how complex, end up with a simple yes or
0:40
no answer, or as computers like
to think of it, true or false.
0:46
JavaScript provides lots
of ways to test things.
0:50
We've seen the triple equals operator,
0:54
which is a way to test
the equality of two things.
0:56
You can use that operator to see if the
value a user typed matches a particular
0:59
string or if the value in
a variable is a particular number.
1:03
JavaScript provides other
comparison operators to help with
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conditional statements.
1:10
Some of them you might
already know from math.
1:12
For example, the greater than and
less than symbols are often used for
1:14
comparing numeric values.
1:18
For instance,
1:19
you can make a game harder if
the player's score is greater than 1000.
1:20
Or on the other hand,
if a visitor is less then a certain age,
1:24
you can tell them to come
back when they are older.
1:27
To get some practice understanding
conditions, let's look at a few examples.
1:30
In the JavaScript console, I'll start by
typing a few conditions greater than and
1:35
less then operators and you try to
decide if a condition is true or false.
1:40
First, 3 is greater than 2, this is true,
because 3 is a larger number than 2.
1:44
Next, 100 is greater than 100,
this is false,
1:52
because the two values are the same,
100 isn't greater than itself.
1:56
How about 100 is greater than or
equal to 100?
2:02
Well, this is true, because although
the value on the left isn't
2:07
greater than the value on the right,
it's still equal to it.
2:11
Here's another one,
negative 12 is less than 0.
2:15
And this is true because negative numbers
are smaller than positive numbers or zero.
2:20
Okay, one more, the string apple
is less than the string bear.
2:25
The greater than and less than operators
aren't limited to just numbers.
2:33
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.
2:51
For instance, if you check if
a number string like 100 is
2:56
less than a letter string like Apple,
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a number is less than any letter,
so this returns true.
3:04
JavaScript provides two ways
to test if values are equal,
3:09
the double equal sign and
the triple equal sign.
3:13
The double equal sign is
called the equality operator.
3:16
It lets you test if two
values are the same, but
3:19
makes some allowances for
different types of values.
3:22
For example, 3 inside quotes is a string,
and 3 without quotes, it's a number.
3:26
But if you use the double equal sign,
3:33
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.
3:46
The triple equal sign is called
a strict equality operator,
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it compares the type as well as the value.
3:55
For example,
a strict comparison like this is false,
3:58
because one value is a string and
the other is a number.
4:02
They are not the same type of value,
so they are not equal.
4:05
It might seem like using the double
equals operator is better since it's more
4:09
flexible.
4:13
However, JavaScript developers tend
to use the triple equals operator and
4:14
avoid the double equals, why?
4:18
Well, you can get into some weird
situations using the double equals
4:21
operator.
4:24
Here's one example,
an empty string is equal to 0.
4:24
This returns true, an empty string
is equal 0, strange isn't it?
4:30
And you can learn why this happens in
the teacher's notes with this video.
4:35
But notice, that if you use a strict
equality operator, the result is false.
4:38
In many cases, the two equality
operators work the same, but
4:44
there are a few cases,
like the one I just showed you,
4:47
where the double equal sign
might get you in trouble.
4:50
So for that reason, I'll use strict
equality or the triple equals operator for
4:53
the rest of this course.
4:58
All right, now,
4:59
let's look at a few examples using
the strict equality operator.
5:00
165 === 165.9, this is false,
5:04
because the two numbers are not equal.
5:09
How about the ' Python ' === the " HTML '?
5:14
This is also false because those
strings have different letters in them.
5:21
Whereas ' JavaScript ' ===
' JavaScript ' is true,
5:29
because those strings
are exactly the same.
5:34
But remember that JavaScript
is case sensitive.
5:38
So comparing Javascript in all lowercase,
5:41
with JavaScript as it's
normally written is false,
5:44
because the first string has all lowercase
letters, and the second does not.
5:48
A lowercase j isn't
equal to an uppercase J.
5:54
JavaScript also provides ways to test
whether two values are not equal.
5:59
There's the not equal or
inequality operator.
6:03
It's an exclamation mark
followed by an equal sign.
6:06
The exclamation point is called a logical
NOT operator, so != means not equal to.
6:09
But keep in mind that it's better to use
the strict inequality operator with two
6:15
equal signs, for
6:19
the same reasons, it's better to use
the strict equality comparison operator.
6:20
So let's look at a few examples of
the strict inequality operator.
6:24
First, 10 !== 9,
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this is true because 10 is not equal to 9.
6:32
How about ' 10 ' !== 10?
6:37
This is also true because the value
on the left is a string, and
6:42
the value on the right is a number,
so the two types do not match.
6:46
Let's check if 'Java' !==
6:50
'java' in all lowercase.
6:55
And this is true,
because the uppercase J in the first
6:59
string isn't the same as
the lowercase j in the second string.
7:03
Finally, negative 59 !== negative 59,
well,
7:08
this is false,
because the two numbers are the same.
7:13
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