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if Statement

An if statement accepts an expression with a set of parentheses ( ):

  • If the expression evaluates to a truthy value, then the code within its code body executes.
  • If the expression evaluates to a falsy value, its code body will not execute.
const isMailSent = true; if (isMailSent) { // This code block will be executed console.log('Mail sent to recipient'); }

else Statement

An else block is added to an if block or series of if-else if blocks. The else block will be executed only if the if condition fails.

const isTaskCompleted = false; if (isTaskCompleted) { console.log('Task completed'); } else { console.log('Task incomplete'); }

NOT ! Operator

The ! operator can be used to do one of the following:

  • Invert a Boolean value.
  • Invert the truthiness of non-Boolean values.
// example 1 let value = true; let oppositeValue = !value; console.log(oppositeValue); // false // example 2 const emptyString = ''; !emptyString; // true const truthyNumber = 1; !truthyNumber // false

JavaScript Comparison Operators

JavaScript comparison operators are used to compare two values and return true or false depending on the validity of the comparison. Comparison operators include:

  • strict equal (===)
  • strict not equal (!==)
  • greater than (>)
  • less than (<)
  • greater than or equal (>=)
  • less than or equal (<=)
1 > 3 // false 3 > 1 // true 250 >= 250 // true 1 === 1 // true 1 === 2 // false 1 === '1' // false

JavaScript Strict Comparisons

The strict equality operator (===) checks if two values are the same and returns true if they are the same. The inequality comparison operator (!==) check if two values are different and return true if they aren’t the same.

console.log(1 === 1); // true console.log('1' === 1); // false console.log(8 !== 9); // true

if else else if Statement

After an initial if block, else if blocks can each check an additional condition. An optional else block can be added after the else if block(s) to run by default if none of the conditionals evaluated to truthy.

const size = 10; if (size > 100) { console.log('Big!'); } else if (size > 20) { console.log('Medium'); } else if (size > 4) { console.log('Small'); } else { console.log('Tiny'); } // 'Small'

AND && Operator

The logical AND operator && checks two values and returns a boolean. If both values are truthy, then it returns true. If one, or both, of the values is falsy, then it returns false.

true && true; // true 1 > 2 && 2 > 1; // false true && false; // false 4 === 4 && 3 > 1; // true

OR || Operator

The logical OR operator || checks two values and returns a boolean. If one or both values are truthy, it returns true. If both values are falsy, it returns false.

true || false; // true 10 > 5 || 10 > 20; // true false || false; // false 10 > 100 || 10 > 20; // false

switch Statement

JavaScript’s switch statements provide a means of checking an expression against multiple values. It first evaluates an expression. The result of the expression is matched against values in one or more case clauses. If a case matches, the code inside that clause is executed.

The case clause should finish with a break keyword. If no case matches but a default clause is included, the code inside default will be executed. If break is omitted from the block of a case (or the execution is not broken otherwise, such as returning from a function with a switch), the switch statement will continue to check against case values until a break is encountered or the flow is broken.

const food = 'pizza'; switch (food) { case 'oyster': console.log('Enjoy the taste of the sea'); break; case 'pizza': console.log('Enjoy a delicious pie'); break; default: console.log('Enjoy your meal'); } // Output: 'Enjoy a delicious pie' // If food = 'Cheese', Output: 'Enjoy your meal'

JavaScript Ternary Operator

The ternary operator allows for a compact syntax in the case of binary (choosing between two choices) decisions. It accepts a condition followed by a ? operator, and then two expressions separated by a :. If the condition evaluates to truthy, the first expression is executed, otherwise, the second expression is executed. It can be read as “IF condition THEN expression1 ELSE expression2”.

let price = 10.5; let day = "Monday"; // The following examples produce the same result: // A: if/else if (day === "Monday") { price -= 1.5; } else { price += 1.5; } // B: ternary operator day === "Monday" ? price -= 1.5 : price += 1.5;