This article contains coding hints and mini examples about JavaScript. You may find them helpful during your JavaScript language exploration on codeguppy.com.
- Variables
- if statement
- For loop
- While loop
- Do While loop
- Switch statement
- Functions
- Array methods
- String methods
- Random numbers
- Modules
Declaring variables
Variables are used to store data such as numbers, strings (text) or even complex objects. Remember:
- You can have as many variables as you want inside a program.
- You need to name each variable with a name that represents the data it stores.
- Give different names to variables inside the same code block (e.g. whats between
{ ... }
) or even inside a function
Declare variable x
let x;
Declare x and initialize it with a numerical value
let x = 1;
Declare s and initialize it with a string
let s = "Hello, World!";
Assigning values to variables
Once a variable has been declared with let
it can be assigned / reassigned with different values as many times as you want.
You can assign it with simple constants or even complex expressions that include constants, other variables and even the same variable! Computers are very good at evaluating expressions.
Assign number 100 to variable x
x = 100;
Assign string "Hello" to variable s
s = "Hello";
Assign an empty array to variable ar
ar = [];
Assign an array of 3 numbers to variable ar
ar = [1, 2, 3];
Assign and array of 2 strings to variable ar
ar = ["A", "B"];
Assign an inline object to variable o
o = { Type: 'car',
x : 100,
y : 200
};
Variable sum is equal to a + b
sum = a + b;
Assign an expression to variable avg
avg = (a + b) / 2;
Variable sum is increased by 10 (the new sum becomes the older sum + 10)
sum = sum + 10;
Variable i is increased (incremented) by 1
i++;
Variable i is incremented by 2
i += 2;
If statement
if
statements are great for controlling the flow of the program. Normally a program is executed one instruction at a time, from top to bottom.
if
allow to take a decision and execute a set of instructions if the condition is met.
Executes the block of instructions between {} if condition is true
if (mouseX < width)
{
}
Executes the first block of instructions if condition is true, otherwise the second block
if (hour < 12)
{
}
else
{
}
Executing different blocks based on different conditions
In the following example, if the first condition is true, then the first block will be executed and the others not.
However, if the first condition is not true, the else if
is used to test another condition, and if is true, the block of that else if
is executed.
The block after the last else
is executed only if no other condition was true until that point.
if (minute <= 15)
{
}
else if(minute <= 30)
{
}
else
{
}
Note: You can have multiple else if
blocks in this kind of experessions.
For loop
Prints numbers from 0 to 4 using a for loop and println
for(let i = 0; i < 5; i++)
{
println(i);
}
Prints numbers from 10 down to 0 using a for loop
for(let i = 10; i >= 0; i--)
{
println(i);
}
Prints even numbers from 0 to 100
for(let i = 0; i <= 100; i+=2)
{
println(i);
}
Print all elements of an array
let ar = [10, 20, 30];
for(let element of ar)
{
println(element);
}
While loop
Print numbers from 0 to 9 using a while
loop
let i = 0;
while(i < 10)
{
println(i);
i++;
}
Do While
Print numbers from 0 to 10 using a do while
loop
let i = 0;
do
{
println(i);
i++;
}
while(i < 10)
Note: do while
loop places condition after the code block, therefore the block can execute at least once even if the condition is false.
Switch Statement
A switch
statement is another instruction besides if
/ else if
for controlling the flow of a program. You can use switch to compare an expression against different values and then run the coresponding set of instructions based if that expression is equal to any case
value.
Usually switch
is used less often than if
/ else if
/ else
.
switch(myExpresion)
{
case 100:
//...
break;
case 200:
//...
break;
case 300:
//...
break;
default:
//...
}
Functions
Functions are great for creating new language instructions
that you can use over and over again in a program.
Once you define a new instruction, it becomes indistinguishable from the built-in instructions present in JavaScript and codeguppy.com
Defining and calling the function balloon
// Function balloon draws a balloon using simple shapes such as circle and line
// It expects as arguments the coordinates for balloon center and the color of the balloon
function balloon(x, y, shapeColor)
{
let r = 30;
let stringLen = 100;
fill(shapeColor);
stroke(shapeColor);
circle(x, y, r);
line(x, y + r, x, y + r + stringLen);
}
// Call function balloon with different parameters
balloon(100, 100, "red");
balloon(300, 300, "blue");
balloon(500, 200, "yellow");
Functions that return values
function addNumbers(x, y)
{
return x + y;
}
// Call a function
var sum = addNumbers(100, 200);
println(sum);
Note: codeguppy.com includes a big number of built-in functions such as circle
, rect
, etc. You can call these functions in the same way you're calling your own custom function.
Array methods
Use an array to conveniently store a series of values using a single variable name. An array has properties and methods that allow to manipulate its elements.
Declaring and initializing ar
to an empty array
let ar = [];
Declaring and initializing ar
to an array of 3 numbers
let ar = [10, 20, 30];
Length of an array
let ar = [10, 20, 30];
println("Length of array: ", ar.length);
Append an element at the end of the array
let ar = [10, 20, 30];
ar.push(100);
println(ar);
Insert an element at the beginning of an array
let ar = [10, 20, 30];
ar.unshift(1);
println(ar);
Insert an element at an arbitrary position
let ar = [10, 20, 30];
// 1 -> after element with potion 1
// 0 -> delete 0 elements
// 15 -> insert number 15
ar.splice(1, 0, 15);
println(ar);
Insert an element at an arbitrary position (easy mode)
Note: The insert
array method is present only in codeguppy.com
let ar = [10, 20, 30];
ar.insert(1, 17);
println(ar);
Read the value of element 2
of an array
let ar = [10, 20, 30];
println(ar[2]);
Calculate the sum of elements of an array
let ar = [10, 20, 30];
let sum = 0;
for(let element of ar)
{
sum += element;
}
println(sum);
Assign a different value to al element of an array
let ar = [10, 20, 30];
ar[2] = 100;
println(ar);
Accesing the first element
let ar = [10, 20, 30];
println(ar[0]);
Accessing the last element
let ar = [10, 20, 30];
let len = ar.length;
println(ar[len - 1]);
Accessing the last element (easy way)
Note: The peek
array method is present only in codeguppy.com
let ar = [10, 20, 30];
println(ar.peek());
Remove the first element of the array
let ar = [10, 20, 30];
ar.shift();
println(ar);
Remove the last element of the array
let ar = [10, 20, 30];
ar.pop();
println(ar);
Remove an element at an arbitrary position
let ar = [10, 20, 30];
// 0 -> element index
// 1 -> number of elements to remove
ar.splice(0, 1);
println(ar);
Remove all elements of an array
let ar = [10, 20, 30];
// clear() is CodeGuppy specific
// use ar.lenght = 0; outside CodeGuppy
ar.clear();
println(ar);
Concatenate two arrays
// Merge / concatenate 2 arrays
let ar1 = ["a", "b", "c"];
let ar2 = ["d", "e", "f"];
let ar = ar1.concat(ar2);
println(ar);
Extract a slice of an array
slice()
is an interesting method that can be used to extract a "slice" from an array. The "slice" will be retured as an independent array. The method receives as arguments the index of the first element (inclusive) and the index of the last element that we want in the slice (exclusive):
let ar = ["a", "b", "c", "d", "e", "f"];
// Extracting a 'slice' from an array
let arSlice = ar.slice(2, 4);
println(arSlice);
Joining elements of an array
let ar = ["a", "b", "c", "d", "e", "f"];
// Join all elements in a string using separator ;
let s = ar.join(";");
println(s);
String methods
Just like with arrays, you can access and manipulate independent characters within a string.
Length of a string
let txt = "JavaScript";
println(txt.length);
Iterating all characters of a string
let txt = "JavaScript";
for(let chr of txt)
{
println(chr);
}
Accessing string characters by position
let txt = "JavaScript";
for(let i = 0; i < txt.length; i++)
{
println(txt[i]);
}
Converting text to uppercase
let txt = "JavaScript";
txt = txt.toUpperCase();
println(txt);
Converting text to lowercase
let txt = "JavaScript";
txt = txt.toLowerCase();
println(txt);
Determine if the string contains another substring
let txt = "Coding is cool!";
let search = "cool";
if (txt.includes(search))
{
println(search + " was found in " + txt);
}
Determine if the string starts with a specified prefix
let txt = "JavaScript is cool!";
let search = "JavaScript";
if (txt.startsWith(search))
{
println(txt + " starts with " + search);
}
Determine if the string ends with a specified sufix
let txt = "JavaScript is cool!";
let search = "!";
if (txt.endsWith(search))
{
println("It is an exclamation!");
}
Find the position of a substring. Search starts at the beginning
let txt = "JavaScript is cool!";
let search = "cool";
let foundAt = txt.indexOf(search);
if (foundAt < 0)
println("Not found!");
else
println("Found at position " + foundAt);
Find the position of a substring. Search starts at specified index.
let txt = "JavaScript is cool! Super cool!";
let search = "cool";
let startAt = 18;
let foundAt = txt.indexOf(search, startAt);
if (foundAt < 0)
println("Not found!");
else
println("Found at position " + foundAt);
Extract a substring from the string
let txt = "JavaScript is cool!";
let index1 = 14;
let index2 = 18;
let txt2 = txt.substring(index1, index2);
println(txt2);
Remove whitespaces from beginning and end of the string
let txt = " I love coding ! ";
txt = txt.trim();
println("'" + txt + "'");
Remove whitespaces from beginning of the string
let txt = " I love coding ! ";
txt = txt.trimStart();
println("'" + txt + "'");
Remove whitespaces from the end of the string
let txt = " I love coding ! ";
txt = txt.trimEnd();
println("'" + txt + "'");
Pads the start of the string with another string
let no = 3;
let txt = no.toString(2).padStart(8, '0');
println(txt);
Pads the end of the string with another string
let n1 = "1";
let n2 = "3";
txt = n1 + "." + n2.padEnd(4, '0');
println(txt);
Codes of characters
let txt = "JavaScript";
for(let chr of txt)
{
// Obtain the Unicode code point value
// ... identical to ASCII code for the range of ASCII values
let code = chr.codePointAt(0);
let line = chr + "\t" + code.toString() + "\t" + code.toString(16).toUpperCase() + "\t" + code.toString(2).padStart(7, "0");
println(line);
}
Characters from codes
let msg = "73 32 76 79 86 69 32 67 79 68 73 78 71"
let base = 10;
let arMsg = msg.split(" ");
for(let i = 0; i < arMsg.length; i++)
{
if (!arMsg[i])
continue;
let code = parseInt(arMsg[i], base);
// Obtain the character from the Unicode code point
// (the Unicode code point is the same with ASCII code for the range of ASCII values)
let chr = String.fromCodePoint(code);
println(chr);
}
Random numbers
Random numbers are extremly useful in coding.
To obtain a random number in JavaScript between 0
(inclusive) and 1
(exclusive) you can use Math.random()
function.
let r = Math.random();
println(r);
codeguppy.com extends the support for random numbers with additional instructions that let you quickly pick a random number in the prefered range.
Random floating point number between 0 and 1 (1 not included)
This is the same as Math.random()
let n = random();
println(n);
Random floating point number between 0 and n (n not included)
let n = random(100);
println(n);
Random floating point number between n1 and n2 (n2 not included)
let n = random(-100, 100);
println(n);
Random int between min and max (both included)
You can use either randomInt
or randomNumber
let n = randomInt(0, 10);
println(n);
Random char between chr1 and chr2 (both included)
function randomChar(chr1, chr2)
let char = randomChar("A", "Z");
println(char);
Random element of an array
let ar = ["J", "a", "v", "a", "S", "c", "r", "i", "p", "t"];
let char = random(ar);
println(char);
Shuffle an array
let ar = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
let ar2 = ar.shuffle();
println(ar2);
Modules
To better organize your code, especially in bigger programs, codeguppy.com introduces the concept of modules.
Instead of writing all the functions of a program in a single code page, you can split them into several code pages, each code page becoming in this way a module.
A module provides strong encapsulation for variables and functions defined inside. This encapsulation allows you to define functions / variables with same name in different modules.
To use the functions inside a module, you need first to require
that module.
Main program
const math = require("MathUtils");
let sum = math.add(2, 3);
let prod = math.prod(3, 4);
println(sum);
println(prod);
Module MathUtils
content
function add(a, b)
{
return a + b;
}
function prod(a, b)
{
return a * b;
}
Note: Another use for code pages is for defining game scenes. codeguppy.com has a built-in game scene manager. Please refer to the "Games" article for more details.
codeguppy.com is using the p5.js library at runtime. Advanced users can leverage almost the entire p5.js functionality. If you are familiar with p5.js, please check codeguppy for p5.js connoisseurs to see how to properly use it in your codeguppy.com programs.
This article is part of a series of mini-articles containing JavaScript coding hints applicable to codeguppy.com environment.
Top comments (1)
Awesome...