Learn JavaScript Properly 1-5 Codecademy JS Track (B)

3. LOOP

‘FOR’ Loops

Doing repetetive jobs. Use loops.

for loop syntax:

for(initiation; condition; incrementation){
    DoThis;
}

(Use i += 1, to replace i++).

arrays

to store lists of data, (mix data type is allowed.)
Position of a data is fixed and ordered.
Make an array: var arrayName = [ ];
index number starts from “0”.

Use for loop for array:

var arrayCity = ["a", "b", "4', "c"];
for (i = 0; i < arrayCity;i += 1) {
    console.("I Love you!");
}

The “i” suggested to be used as “iterator”.

Little project “search for your name”

Variable declaration:

var text = "Hey, how are you \
doing? My name is Emily. Emily loves to swim.";
var myName = "Emily";
var hits =[];

(the back slash “\“ is to mark a line break.)

Write the for loop to loop through letters in “text”:
for(i = 0; i < text.length; i += 1) {
}
put the if statement inside the for loop to search for the first letter of “myName”:
if (text[i] === myName[0]){
}
Add another for loop inside the if statement push the letters into array “hits”:
for(j = i; j <= (myName.length + i) ; j += 1) {
hits.push(text[j]);
}
Log it if no hit:
if (hits[0] === ""){
console.log("Your name wasn't found!");
} else {
console.log(hits);
}
another way for the condition:
if(hits.length === 0)
And it’s done!
-Think about how to fine-tune it, make sure it only finds the exact matches for you name. How to print out your name in a single string.(search on internet to see if there’s already any JS program to do this.)

‘WHILE’ Loops

while loop is used when we don’t know in advance how many times we need to loop. Or we want to randomly loop through some code. Ex: coin flips….
The syntax is:
while(condition){
ACTION;
}
If we use numbers inside ofthe condition. 1 means “true”, 0 means “false”. Ex: while(myCondition === 1) means “while myCondition is true”.
Actually we can just put the variable as condition, and it means that variable is true. Ex: while(myCondition) is the same as while(myCondition === 1).
Pay attention to not creating “infinite loop”.

Set/initiate the condition outside of the loop. Ex:

var myCondition = 0;
while(myCondition < 10){
    ACTION;
}

for or while is sometimes a matter of preference.

‘do’ / ‘while’ loop

To run the code at least ONCE!
Syntax:
do {
ACTION;
} while (condition);
It reads “Do the ACTION once, while the condition is true loop through the ACTION untill the condition becomes false.”

Exercise “Dragon Slayer” game

ALWAYS start with variables declaration:
1.Checker if we’re still slaying. 2.checker if we hit the dragon. 3.damage tracker. 4.total damage tracker.

var slaying = true;
var youHit = Math.floor(Math.random() * 2);
// Math.floor(x) function set the number to the largest intenger less than or equal to x.
// Math.random() function randomly pick a floating point number between 0 (include) and 1(exclude).
// So "youHit" will be set to 0 or 1 randomly.
var damageThisRound = Math.floor(Math.random()*5 + 1);
// "damageThisRound" will be a random number between 1 and 5.
var totalDamage = 0;

Add then while loop to start attacking! (Put the action “slaying = false” to make it exit the loop.)
while(slaying){
slaying = false;
}

Inside the while loop, if you hit the dragon?

if(youHit){
    console.log("Hit!!!!!");
} else {
    console.log("RIP.....");
}

if(youHit) set “totalDamage” equal to “totalDamage + damageThisRound”.
And create another if statement, check if totalDamage >= 4, if true, print “You finished it!”, else try to get another random “youHit” value, and loop again.
totalDamage += damageThisRound;
if(totalDamage >= 4) {
console.log("You win!");
slaying = false;
} else {
youHit = Math.floor(Math.random() * 2);
}
AND IT’s DONE!!!