This challenge will cover the lessons learned from Chapter 2 of the Eloquent Javascript Book link. I recommend you to go ahead an read through the chapter yourself, but this tutorial will give you the bare essentials.
After this section you will finally be able to write something that can be called a program.
An expression is code that produces a value and statements is a single unit of code that can be executed.
for example: !false; is a statement and it has the expression !false
In Javascript there is a keyword called var, this allows you to store data into variables.
for example: var myName = "John Kim";
Now if I want to access the string "John Kim" I can simply refer to the variable myName
for example: console.log("hello my name is", myName);
There are other keywords that allows your to store variables, such as let and const but we will go over that in another lesson.
In Javascript there are a list of keywords that should not be used as variable names.
Here is the full list. You do not need to remember all of them right now.
break case catch class const continue debugger default delete do else enum export extends false finally for function if implements import in instanceof interface let new null package private protected public return static super switch this throw true try typeof var void while with yield
All of these keywords are part of Javascript and they have specfic uses for them. For example we have used typeof multiple times in the previous challenge.
functions are a very important concept in programming. Just think of functions as small programs that are packaged up and ready to be used.
The anatomy of a function is as follows:
functionName (argument) { code goes here }
you can then execute this function by invoking it with () for example functionName() would invoke the function.
Javascript also has a handful of built in functions that you can use. Actually we have already been using them in our previous challenges.
the console.log(argument) is a function that takes in a value and prints the value to the terminal.
Before we move on you should understand that not all functions are equal. Please take some time to understand the below two concepts.
pure functions: a function that does not effect anything outside of itself
example:
pureFunc(arg) {
return arg;
}
non pure functions: a function that creates side effects and effects things outside of itself
example:
var count = 1;
nonPureFunc(arg) {
count += 1;
return arg;
}
Notice that no matter how many times the pureFunc is invoked the result and environment is the same. However, when we invoke the nonPureFunc multiple times, the count variable will increment in value every time.
Functions can output a value which is usually called return and the keyword return is used to denote the value that needs to be returned
Imagine for a second if you had one statement after another and they executed in that order without repeating, branching, or looping. In this case you would call this a straight control flow. However, most programs do not follow this straight flow. The following sections describes ways to alter this control flow.
In the conditional execution the program can choose between two Boolean based values.
Below is a simple conditional execution.
var age = 21;
if (age >= 21) {
console.log('welcome to the bar');
} else {
console.log('you are too young to come in');
}
In this example the program will only execute the statement inside the true condition. e.a. console.log('welcome to the bar'); because the age value of 21 meets the conditional.
While and Do Loops is one way for us to repeat execution of some segment of our program.
The loop will continue to repeat the segment of our code until a condition has been made. It is possible to be stuck in a infinite loop so be careful!
var count = 0;
while (count <= 10) {
console.log('the count is', count);
count += 1;
}
The do loop is similar to the while loop but the do loop guarantees that it will execute it's body at least once before looping the body.
TODO: do while example
A For loop is similar to a while loop, but it requires a counter. Basically you are telling the program to execute the segment of the code until a certain count.
for (var i = 0; i <= 10; i++) {
console.log ('the count is', i);
}
the var i = 0 denotes the number to start the count, the i <= 10 denotes the condition when the loop should stop, and finally the i++ denotes the amount to count up by for each step.
NOTE: i++ and i += 1 is a short hand way of writing i = i + 1, also another thing to keep in mind is that you don't need to only update the count by one. For example you can go up by 3, i += 3;
Sometimes you need to forcefully stop the loop before it meets its conditional statement. To do this we use the break keyword
for (var i = 0; i <= 10; i++) {
console.log ('the count is', i);
if (i === 5) {
break;
}
}
In the above example, the loop will stop execution once the if conditional statement has been met.
when you are using the if statements, sometimes the statements can get too long to manage. When this happens, you should use the switch statement. Switch statements are used when you have a condition that can be many different values and it needs to output different results.
var mood = 'happy'
switch (mood) {
case "happy":
console.log('time to go to work');
break;
case "gloomy":
console.log('go work out');
break;
case "sad":
console.log('call your mom');
default:
console.log('work on something amazing');
break
}
Things to note for switch statements is that you need to add a break
statement after each case statement. also you need to a default case for when the value doesn't meet any of the other cases.
Don't write fake comments. This is kinda of a joke but comments should be used sparingly as your code should read like well written pros. More on this later. Comments are denoted using the //
// this is a comment
You can also comment multiple lines by surrounding /* and */
/*
this is a multiple line comment.
here is another line.
*/
In this challenge we will practice control flows. Using any form of looping, console log a number from 0 to 100.
FizzBuzz is one of the most famous interview questions. It is mainly used as a sanity check as someone who cannot solve this problem generally will raise red flags as someone who does not have a foundation understanding of programing.
The FizzBuzz Challenge from the Book: Write a program that uses console.log to print all the numbers from 1 to 100, with two exceptions. For numbers divisible by 3, print "Fizz" instead of the number, and for numbers divisible by 5 (and not 3), print "Buzz" instead. Also for numbers that are divisible by both 3 and 5 print "FizzBuzz" instead.