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JavaScript provides ways to combine two or more strings into a single string, and it's something you'll likely do a lot in programming. There are different techniques for combining strings in JavaScript. First, learn how to add strings together using a process called "concatenation."
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JavaScript provides ways to combine two or
more strings into a single string, and
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it's something you'll likely do a lot and
programming.
0:05
For example, you might collect
the user's first name as one string and
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their last name as a separate string.
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To display the user's full name on the
page, you need to combine the two strings.
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And what if you want to display
their full name within a message?
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You'd have to combine the first and
last name strings with the message string.
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There are different techniques for
combining strings in JavaScript.
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First, I'll teach you how to add
strings together using a process
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called concatenation.
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String concatenation is
the process of combining or
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adding two or more strings together
to create a bigger string.
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One way to concatenate strings in
JavaScript is with the + operator.
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For example, by adding the string
my favorite to the string movies,
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we end up with one longer string.
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In JavaScript,
you'll often need a string to hold a value
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that you can't predict
until your program runs.
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For example, if you want your
program to greet someone by name,
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you might store the greeting
Hello in a variable.
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Well, you cannot know the person's
name ahead of the time.
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So your program need to combine the stored
Hello with the person's name at the time
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the program collects that information
like when they login for example.
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Now, that you've learned the method for
collecting information from a user,
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I will teach you how to use that
input to create different messages.
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We'll do this by combining
the string returned
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by the prompt method with another screen.
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Open the file named combine.js
inside your js folder and
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update the script tag in
index.html to point to combine.js.
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Let's start by declaring two variables,
name and message.
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Name will store the value returned
by a prompt dialog that asks,
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What is your name?
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Then assign the message variable,
a string that holds the word Hello.
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Now, let's add the name the visitor
typed into the prompt dialog
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to this string to create a message
like Hello Gil or Hello Anwar.
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Again, one way to combine or concatenate
strings is with the + operator like this.
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Name holds the string returned
by the prompt method.
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So notice how we're literally joining the
two strings together with the + symbol.
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Let's log the value of message to
the console with console.log message.
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If I save the file, and refresh
the browser, the prompt dialog appears.
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I'll type my name, click OK and
see the message in the console.
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But notice that there's no space
between Hello and my name.
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When you combine strings, you're literally
placing them next to each other.
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So if you need a space,
you have to add it.
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I'll go back to my JavaScript file and add
a space at the end of the string Hello,
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I'll save the file,
refresh the page and that looks good.
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When a variable like name contains
a string, adding that variable to
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another string is exactly the same
as combining the two strings.
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In other words,
the variable is really a placeholder for
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the string value stored inside it.
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You can add any number
of strings together.
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For example, I can add another
string to the message value, like so
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period space Welcome to my music site,
And a period and a space.
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I'll save the file,
refresh the browser, enter my name and
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the console display the longer string.
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Hello Guil.
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Welcome to my music site.
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In programming there might be times
when you want to create a long string,
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maybe even an entire paragraph
of text that includes string
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values from several variables.
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In that case, you can use the +
operator over and over, but
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doing that can often make
your code hard to read.
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For example,
I'll concatenate the string, I'm so
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happy that you came by to visit, ,.
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Then concatenate the string
stored in the name variable.
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Then concatenate another string
that holds the text period space.
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Feel free to come again and
listen to more music.
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I'll save the file,
refresh the browser, enter my name,
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and there's the longer string.
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Hello Guil.
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Welcome to my music site.
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I'm so
happy that you came by to visit, Guil.
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Feel free to come again and
listen to more music!
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Good, to make your code easier to read,
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you can create a longer string using
a series of smaller statements.
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For example, I can begin to
rewrite this code like this.
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On the next line,
type message = message + I'm so
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happy that you came by to visit.
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This approach might look familiar,
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the variable message appears
twice in the statement.
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Remember, when putting
a value into a variable,
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whatever's to the right of the equal
sign goes into the variable on the left.
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In this case, what's on the right is
the current contents of the variable
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message added to the string, I'm so
happy that you came by to visit.
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These two strings are combined, and
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then the result is placed back
into the variable message.
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This works like earlier when we added more
points to the current value of the score
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variable.
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For example, in this case, instead of
completely replacing what's inside the box
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labeled message with something else, we're
adding to the current contents of the box.
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And you learned that there's a shorthand
for adding to the contents of a variable.
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Replace this part with a +=,
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or the addition assignment operator.
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Feel free to use whichever
method you like, but
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+= does require a little less typing.
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Next, I'll build up the rest
of the string like this,
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message += the string stored
in the name variable.
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Then on the next line, message +=.
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Feel free to come again and
listen to more music.
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Let's see how this works.
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I'll save the file and
refresh the browser,
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type my name into the prop
dialog then click OK.
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In the console, we're not seeing the final
message instead there is some sort of
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Uncaught TypeError that says,
assignment to constant variable.
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Can you figure out what's
producing this error?
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On this line, we are declaring the message
variable using the keyword const.
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Remember, the value of a variable
declared with const cannot be
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changed through reassignment.
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We're using the addition assignment
operator to reassign message,
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to a longer and longer string value
until we have the final string.
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In this case, we need to use the key
word let, which as you learned lets
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you change or manipulate a variables
value through reassignment.
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Now, let's try it.
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Refresh the page.
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I'll type Guil into the prompt dialog, and
there's the final message in the console.
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Good, you've just learned
some really important skills,
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how to add strings together using
a process called concatenation, and
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how to combine strings with variables
that contain string values.
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