JavaScript Loops

Question 1

What is a Reverse Loop?

Answer 1

A “for” loop can iterate “in reverse” by initializing the loop variable to the starting value, testing for when the variable hits the ending value, and decrementing (subtracting from) the loop variable at each iteration.

Example:
const items = [‘apricot’, ‘banana’, ‘cherry’];

for (let i = items.length - 1; i >= 0; i -= 1) {
console.log(${i}. ${items[i]});
}

// Prints: 2. cherry
// Prints: 1. banana
// Prints: 0. apricot

Question 2

What is a Do…While Statement?

Answer 2

A “do…while” statement creates a loop that executes a block of code once, checks if a condition is true, and then repeats the loop as long as the condition is true. They are used when you want the code to always execute at least once. The loop ends when the condition evaluates to false.

Example:
x = 0
i = 0

do {
x = x + i;
console.log(x)
i++;
} while (i < 5);

// Prints: 0 1 3 6 10

Question 3

What is a For Loop?

Answer 3

A “for” loop declares looping instructions, with three important pieces of information separated by semicolons ; :
1. The “initialization” defines where to begin the loop by declaring (or referencing) the iterator variable.
2. The “stopping condition” determines when to stop looping (when the expression evaluates to “false”).
3. The “iteration statement” updates the iterator each time the loop is completed.

Example:
for (let i = 0; i < 4; i += 1) {
console.log(i);
};

// Output: 0, 1, 2, 3

Question 4

How do you Loop Through Arrays?

Answer 4

An array’s length can be evaluated with the “.length” property. This is extremely helpful for looping through arrays, as the “.length” of the array can be used as the stopping condition in the loop.

Example:
for (let i = 0; i < array.length; i++) {
console.log(array[i]);
}

// Output: Every item in the array

Question 5

What is the Break Keyword?

Answer 5

Within a loop, the “break” keyword may be used to exit the loop immediately, continuing execution after the loop body.

Here, the “break” keyword is used to exit the loop when “i” is greater than 5.

Example:

for (let i = 0; i < 99; i += 1) {
if (i > 5) {
break;
}
console.log(i)
}

// Output: 0 1 2 3 4 5

Question 6

What is a Nested For Loop?

Answer 6

A nested “for” loop is when a “for” loop runs inside another “for” loop.

The inner loop will run all its iterations for “each” iteration of the outer loop.

Example:
for (let outer = 0; outer < 2; outer += 1) {
for (let inner = 0; inner < 3; inner += 1) {
console.log(${outer}-${inner});
}
}

/*
Output:
0-0
0-1
0-2
1-0
1-1
1-2
*/

Question 7

What is a Loop?

Answer 7

A “loop” is a programming tool that is used to repeat a set of instructions. “Iterate” is a generic term that means “to repeat” in the context of “loops”. A “loop” will continue to “iterate” until a specified condition, commonly known as a “stopping condition” is met.

Question 8

What is a While Loop?

Answer 8

The “while” loop creates a loop that is executed as long as a specified condition evaluates to “true”. The loop will continue to run until the condition evaluates to “false”. The condition is specified before the loop, and usually, some variable is incremented or altered in the “while” loop body to determine when the loop should stop.

Example:

while (condition) {
// code block to be executed
}

let i = 0;

while (i < 5) {
console.log(i);
i++;
}