[TIL] 20201202 Repeating Stuff with Loops

Loops

• Allows to repeat code
• There are multiple types
  • for loop
  • while loop
  • for ... of loop
  • for ... in loop

 

 

for Loop

Syntax

for ([initialExpression]; [condition]; [incrementExpression]){
    //code
}

 

Example

for (let i=1; i<=10; i++){
    console.log(i);
} //1 2 3 4 5 6 7 8 9 10

 

 

 

Infinite Loops

• Does not stop
• Make sure the loop stops when it should.

 

 

 

Looping Over Arrays

//Examples

const animal = ['lions', 'tigers', 'bears'];
for (let i=0; i<animal.length; i++){
    console.log(i, animal[i]);
}

//1 lions 
//2 tigers
//3 bears

 

 

 

Nested Loop

Having another loop inside of a loop

 

 

 

while Loop

• Continues running as long as the test condition is true.
• Useful when it's unclear how many times this loop should run.
• Syntax

while(test condition) {
    //code
}

 

 

Break Keyword

Breaks out of the loop immediately as soon as break is encountered.

 

 

 

for ... of Loop

• Easier way of iterating over arrays & other iterable objects (i.e. string, map, set, object...)
• Syntax

for ([variable] of [iterable]) {
    //code
}

• Example

const numbers = {1, 2, 3, 4, 5};

for (let num of numbers) {
   console.log(num);
}

//1 2 3 4 5

 

 

Iterating Over Objects

• Object Literals can't be iterated with for ... of
• There are several ways to iterate over objects.

 

for ... in

• Iterates only the keys
• Syntax

for ([variable] in [object]){
    //code
}

 

Object.keys( )

• Gives an array of keys
• Syntax

Object.keys([object]);

 

Object.values( )

• Gives an array of values
• Syntax

Object.values([object]);

 

Object.entries( )

• Gives an nested array of keys and values
• Syntax

Object.entries([object]);

 

 

 

 

 

 

* This post is a summary of Udemy Course "The Web Developer Bootcamp" by Colt Steele.