Lesson Weekend

Let's dive more into methods. JavaScript offers built-in methods for strings and numbers. Let's take a look at a few of these methods, including some we've learned about already. Note that this list below isn't comprehensive - there are many more methods out there that we'll take a look at soon!

String Methods


toUpperCase

Here's one we've learned already:

> "supercalifragilisticexpialidocious".toUpperCase();
"SUPERCALIFRAGILISTICEXPIALIDOCIOUS"

toLowerCase

Here's the opposite of toUpperCase, making a string all lower case:

> "HOWDY, NEIGHBOR".toLowerCase();
"howdy, neighbor"

concat

Here's the other string method we've learned - a method so important that we recommend memorizing it (though you can always look up the documentation if you need to):

> const word = "foo";
undefined
> word.concat("bar");
"foobar"

charAt

Some string methods take numbers as arguments. Here's an example:

> "caterpillar".charAt(5);
"p"

Did you notice something funny about this example? What's the fifth character of the word "caterpillar"? Well, with the way we normally count, "c" is the first letter, and "r" is the fifth. But JavaScript says that the character at the 5th position is "p". That's because computers start counting at zero. So "c" is the zeroth letter, and "r" is the fourth. This is really important - and it's another thing that trips up beginners. However, it will soon become second nature.

Number Methods


toString

This method turns a number into a string.

> const myBirthday = 42;
> const myStringifiedBirthday = myBirthday.toString();
"42"

We can also call toString on a number instead of a variable:

> 42.34.toString();
"42.34"
> 42..toString();
"42"

Note that you need to add the decimal point after a whole number before you can call toString on it! So that means, there are two decimal points.

toFixed

This method returns a string with only the number of decimal points that is specified in the argument. If you want 1 decimal point, and your number has 3, then toFixed will chop off the extra decimal points, leaving only 1. Note that this method is called on a number, but turns the number into a string.

> 42.222.toFixed(1);
'42.2'
> const myFavRealNumber = 3.14;
> myFavRealNumber.toFixed(0);
'3'

Chaining Methods


Methods can be chained like this:

> "foo".concat("bar").toUpperCase();
"FOOBAR"

We actually tried out chaining these exact string methods when we discussed the distinction between methods and functions. As we can see, when we chain methods together like this, we first concatenate the string and then uppercase that string.

Here's an example of chaining number methods:

> 4.3354.toFixed(2).toString();
"4.34"

In this example, we are first executing toFixed on the number, and then we're turning it onto a string with toString. Take note, it is redundant to call toString after toFixed, because toFixed returns a string anyways.

Concatenation or Arithmetic with the + Operator


The + operator lets us do addition if we're working with numbers, or concatenation if we're working with strings. Using the + with numbers should be familiar:

> 1 + 3
4

Let's take a look at using + with strings:

> "I love" + " " + "Epicodus";
"I love Epicodus"

As we can see, we can just use the + sign to "add" strings together! This has the same effect as the concat method.

And we can do this with variables, too:

> const sentiment = "I love ";
undefined
> const animal1 = "cats";
undefined
> const animal2 = "dogs";
undefined
> sentiment + animal1;
"I love cats"
> sentiment + animal2;
"I love dogs"

Or with variables holding numbers:

> const number1 = 1;
undefined
> const number2 = 99;
undefined
> number1 + number2;
100

Now, check out this more complex example, where we include a variable with a method called on it:

> const myBirthday = 42;
> const aboutMe = "I am " + myBirthday.toString() + " and I was born in '79.";
> aboutMe;
"I am 42 and I was born in 1979."

Here's the same example written in a different way:

> "I am " + 42.toString() + " and I was born in '79.";
"I am 42 and I was born in 1979."

Terminology


  • Chaining methods: Calling a method directly on the return value of another method.
"foo".concat("bar").toUpperCase();
  • Concatenation: Combining two Strings together into one String. You can combine strings with + instead of concat(). This is still known as concatenation despite not using the concat() method:
"I love" + " " + "Epicodus";

Methods


A few useful string methods:

  • charAt(); - Returns the character at a particular location in a String.
  • toUpperCase(); - Converts a string to uppercase.
  • toLowerCase(); - Converts a string to lowercase.
  • concat(); - Combines two strings.

A few useful number methods:

  • toString(); - Converts a number into a string.
  • toFixed(); - Converts a number into a string with only the number of decimal points that is specified in the argument.

Other Notes


You can call methods on strings or numbers, or variables assigned to strings or numbers:

"supercalifragilisticexpialidocious".toUpperCase();
const word = "foo";
word.concat("bar");

You might wonder how we were able to use concat with a constant, but this method (and most others) doesn't change what's known as the receiver - the thing that a method is being called on. In the example above, word is the receiver. And if we check the value of word, it's still "foo", not "foobar". We would need to assign the return value of the expression above to a new variable for "foobar" to be saved.

Lesson 13 of 65
Last updated May 23, 2022