This article is about one of JavaScript's primitive data types, String. Strings are what you'll use to represent textual data. This means that strings are useful in representing things like messages, names, poems, and so on. A string is a sequence of characters.
Strings are always wrapped by a pair of single quotation marks (') or by a pair of double quotation marks ("). Between the enclosing quotation marks, you can put any characters! Here are six examples of strings:
"potato";
"New York";
"azablan@appacademy.io";
"Follow the yellow brick road, please!";
"365 days a year";
"";
Above, notice that you are free to mix in any characters into a string. This includes spaces, numerics, punctuation, and other symbols. The sixth string above is the empty string; it contains zero characters!
You are probably wondering why you are allowed to use either single or double quotes when denoting a string - why is this useful? Maybe you want a string that contains quotation marks:
// VALID strings:
'Shakespeare wrote, "To be or not to be"';
"That's a great string";
// INVALID string:
'That's a bad string'
If you want to use a single quote as a character of a string, you simply need to enclose the string in double quotes, and vice versa.
Since a single string can contain any number of characters, you may find it useful to count the number of characters in a string using .length:
console.log("ramen".length); // => 5
console.log("go home!".length); // => 8
console.log("".length); // => 0
Strings consist of multiple characters. These characters are numbered by indices starting at 0. So in the string 'bootcamp', 'b' is at index 0, 'o' is at index 1, 'o' is at index 2, 't' is at index 3, and so on. You can look at particular characters of a string by using [] and specifying an index:
console.log("bootcamp"[0]); // => 'b'
console.log("bootcamp"[1]); // => 'o'
console.log("bootcamp"[2]); // => 'o'
console.log("bootcamp"[3]); // => 't'
console.log("bootcamp"[7]); // => 'p'
console.log("bootcamp"[10]); // => undefined
console.log("bootcamp"[-3]); // => undefined
In general, when you index a string using the expression string[i], you get back the single character at position i. Looking at the last two examples above, if you use an invalid index with a string, the value returned is undefined. This makes sense because there is no character at the given position! It's also worth mentioning that an index should always be a number.
Bear in mind that indices begin at 0 and not 1! Forgetting this nuance can lead to incorrect code for both new and experienced programmers alike. Let's hone in on an important distinction: the index of the last character of a string is always one less than its length.
console.log("cat".length); // => 3
console.log("cat"[3]); // => undefined
console.log("cat"[2]); // => 't'
In other words, although the length of 'cat' is 3, the index of the last character ('t') is 2.
You can also calculate the index of a given character within a string by using indexOf:
console.log("bagel".indexOf("b")); // => 0
console.log("bagel".indexOf("a")); // => 1
console.log("bagel".indexOf("l")); // => 4
console.log("bagel".indexOf("z")); // => -1
If you attempt to search for a character that is not present in a string, indexOf will return -1. This makes sense because -1 is not a valid string index. The smallest index possible is 0!
If you search for a character that appears more than once in a string, indexOf will return the index of the first occurrence of that character.
You can also use indexOf to search for a substring of characters. Under this circumstance, indexOf will return the index where the substring begins in the main string:
console.log("door hinge".indexOf("oor")); // => 1
console.log("door hinge".indexOf("hi")); // => 5
console.log("door hinge".indexOf("hint")); // => -1
Concatenation is just a fancy word for joining strings together into a single string. To concatenate strings, you use the + operator:
console.log("hello" + "world"); // => 'helloworld'
console.log("goodbye" + " " + "moon"); // => 'goodbye moon'