| Interactive Media Design

Unary Operators

Unary operatorsopen in new window require only one operand to perform an operation.

The delete Operator

The delete operatoropen in new window is used to delete an object's property or an element at a specified index in the array.

NOTE

When using the delete operator on an array, the array is NOT reindexed and the length is not changed. Therefore, using the delete operator with arrays is generally discouraged. Use the splice() method instead.

const person = {
  name: 'Ted',
  age: 21
}

console.log(person) // {name: 'Ted', age: 21}
delete person.age
console.log(person) // {name: 'Ted'}

const colors = ['red', 'green', 'blue']

console.log(colors) // ['red', 'green', 'blue']
delete colors[1]
console.log(colors) // ['red', undefined, 'blue']

The typeof Operator

The typeof operatoropen in new window returns a string indicating the type of the following operand.

const name = 'Ed'
const pi = 3.14
const enrolled = true

console.log(typeof 'Ted')               // string
console.log(typeof name)                // string
console.log(typeof 21)                  // number
console.log(typeof pi)                  // number
console.log(typeof ['red', 'green'])    // object 
console.log(typeof {name: 'Ted'})       // object
console.log(typeof true)                // boolean
console.log(typeof enrolled)            // boolean
console.log(typeof undeclaredVariable)  // undefined

Before the introduction of ES2015, typeof was a guaranteed safe way to return a the datatype of a variable, even with undeclared variables. But with introduction let and const, which use block-scope, a ReferenceError can occur if the variable is declared after the typeof operator is used on the same variable.

console.log(typeof undeclaredVariable)  // undefined
console.log(typeof name)                // ReferenceError

const name = 'Ted'