Learn JavaScript - Conditionals, Loops, Array

true

4 is greater than 1, so the expression evaluates to true. 4 and 1 are referred to as the operands and > is the operator.

true

The "chatty" strings both have the same length and the same elements in the same order, so the === operator returns true.

true

The number 3 is less than or equal to 300.

"This code is executed"

The boolean condition 5 === 5 evaluates to true, so the code in the block is executed. The code block is delimited by {}.

Nothing is printed to the console because the boolean condition is false. When the boolean condition is false, the code in the code block is not executed.

"walking dead"

When the boolean condition evaluates to false (5 > 10), the code block associated with the if keyword is not executed and the code block associated with the else keyword is executed.

"just chill, have fun"

is printed to the console as the boolean condition associated with the else if clause is true.

"I like peanuts" is printed to the console. 5 does not equal true or false, but it is considered "truthy" in a boolean context. Type Boolean(5) in the console to see if the number 5 is considered truthy or falsey. In JavaScript, undefined, NaN, null, 0, "", and the keyword false are all false in a boolean context. All other values are truthy.

"party hard!"

"party hard!" is printed to the console because "cool" is truthy. "program more" is not printed to the console because the empty string is falsey.

true

The ! operator returns the opposite of the boolean value it is prepended to.

"This syntax is weird..."

!undefined is true in a boolean context, so the code block associated with the if statement is executed. The code block is not delimited with {} because the curly brackets are optional when the code block is on the same line as the if statement. For multi-line code blocks, the curly brackets are required.

The counter is at 0
The counter is at 1
The counter is at 2

A while loop will execute the block as long as the boolean condition evaluates to true.

10

The for loop initializes a loop variable, specifies when the loop should terminate, and increments the loop variable. For loops are a convenient way to loop through arrays.

"bob"

The first statement initialized the array and assigns it to the variable my_array. Arrays are zero-indexed, so the first element is in position zero, the second element is in position one and so forth. The [] syntax is used to access elements in arrays.

[555666, "quack", true]

Variables can be used to represent elements in an array. Also notice that arrays can contain elements with different types. The array in this example contains one number, one string, and one boolean value.

3

All arrays have a length property which represents the number of elements in an array.

["bob", 23, false];
// OR
new Array("bob", 23, false);

Both answers create arrays with the same elements, but the first example uses Array literal notation and the second example uses a constructor function. Other quizzes will cover constructor functions in detail.

"marker"

writing_tools.length evaluates to 3 and writing_tools.length - 1 evaluates to 2. The final element of the array has an index equal to the length of the array minus one.

["master p", 2];

Array elements can be updated by indexing an element of the array and setting the value to something new.

20

The while loop iterates over every element in the numbers array and updates the sum variable with each iteration.

"teenage mutant ninja turtles "

The great_show variable is initially assigned to the empty string and is updated with the strings in the word array plus a space for each iteration of the for loop.

"object"

Arrays are a special type of object. Later quizzes in this series will cover objects in greater detail.

false

The two arrays being compared with the === operator have the same elements, but they are different arrays, so false is returned. The === only returns true when comparing arrays if the operands are exactly the same array.

true

In this example, the === operator is comparing two variables that point to the same exact array, so true is returned.

var result = 0; 
for (var i = 0; i < weird.length; i++) {
  var element = weird[i];
  if (typeof(element) == "number") { result += element };
}
console.log(result);

All elements from the weird array are looped through and added to the result variable if they are numbers.

The falsey values are the empty string, 0, the keyword false, undefined, and null. In a boolean context, falsey values are treated as false (falsey values don't necessarily equal false).

var result = "";
for (var i = 0; i < heaven.length; i++) {
  var element = heaven[i];
  if (element[0] == "b") { result += element + " " };
}
console.log(result);

Strings can be indexed, similar to arrays.