Strings¶

All of the functions you have seen so far have worked with numbers or boolean (true/false) values. Strings are the other main type of data that you will be transforming with ClojureScript.

Defining Strings¶

A string is simply any set of characters between double quotes.

"This is a string."
"Multi-language strings: México Россия 日本."
"Strings can extend
across multiple lines"


If you need to put a double quote mark inside a string, you must escape it by using the backslash character. You also use backslash to include new line characters (\n) or tab characters (\t) in a string:

"Please type \"goodbye\" to exit."
"The \\ character is not often seen alone."
"Tabs\tspace\tthings\tout."
"multiple\nlines"


Try typing each of these as the definition of message in the following active code to see how it works.

Combining Strings¶

The str function constructs a single string from its arguments. If the argument is not a string, it will be converted to one.

(str "cow" "bell") → "cowbell"
(str "The band has " (* 38 2) " trombones.") → "The band has 76 trombones."
(str "Is 3 more than 5? " (> 3 5)) → "Is 3 more than 5? false"
(str 12 34) → "1234"
(str 56 "78") → "5678"


Because ClojureScript compiles to JavaScript, you might be tempted to use the + function to add strings together. This works, but I advise against it. Leave the plus sign for adding numbers, and use str for combining strings.

JavaScript String Manipulation¶

JavaScript has a whole host of functions for dealing with strings, and you call them in exactly the same way that you call any other JavaScript function Here are a few of them:

• (.toUpperCase string) returns a new string that is the string with letters converted to upper case.
• (.indexOf string part) returns the position of part in string; if the part isn’t in the string, returns -1
• (.replace string oldpart newpart) returns a new string with oldpart replaced by newpart
• (.startsWith string part) returns true if the string starts with part
• (.trim string) returns a new string with leading and trailing whitespace (blanks, tabs, or new lines) removed

Type the preceding function calls (one at a time) in the following activecode area, given the def that is already there.

(.toUpperCase message)
(.replace message "great" "the best")
(.indexOf message "is")
(.startsWith message "Clojure")


Converting Strings to Numbers¶

As you will see in the section about accessing web pages, when you get information from the person using your program, it will always be in the form of a string. Let’s say your web page asks for a person’s age. When they type 56, what you will get is the string "56", and you have to convert it to numeric form.

You do this by using JavaScript’s parseInt function for integers, or with parseFloat for numbers with decimals. Here’s how you use such functions:

Note

If you do something like this: (js/parseInt "12.95") you will get 12 as a result; parseInt stops as soon as it finds something that couldn’t be part of an integer, so (js/parseInt "99Luftballons") results in 99.

Clojure String Manipulation¶

ClojureScript also lets you use a string manipulation library from its “parent” language Clojure. To use these functions (detailed here), you prefix their names with clojure.string/. Here are some of the Clojure string functions, many of which are similar to those in the preceding section.

• (clojure.string/upper-case string) returns a new string that is the string with letters converted to upper case.
• (clojure.string/replace-first string oldpart newpart) returns a new string with first occurrence of oldpart replaced by newpart
• (clojure.string/replace string oldpart newpart) returns a new string with all occurrences of oldpart replaced by newpart

The clojure.string library doesn’t work in the activecode environment, so this book will stick to the JavaScript string manipulation functions. When you write your own ClojureScript programs, I strongly advise you to use the clojure.string library instead.

Next Section - Accessing Web Pages