`.includes()`

Checks if an element exists in an array or a substring in a string.

Time to read: less than 5 min

Briefly

This method is defined for arrays and strings.

For arrays: checks if the sought element exists in the array.

For strings: checks if the sought substring exists in the string.

Returns true if the sought element was found, and false — if not 😎

Example

The method takes two arguments — the value to check, and the position from which to start checking. The second argument is optional and defaults to 0.

Features of using the second argument

If a positive value or 0 is passed as the argument, the search will start from this index to the end of the array.

If a negative value is passed, the search will start from this index, counted from the end of the array, and will proceed to the end of the array. For this case, the starting index of the search can be calculated using the formula length of array/string + passed negative number. For example, if the length of the array/string is 10, and the passed argument is -2. The search will start at position 8, since 10 + (-2) = 8.

If the second argument is greater than the length of the array/string, the method will always return false.

Array:

        
          
          const dead = ['Jon Snow', 'Joffrey', 'Ned Stark', 'Night King']const isAryaDead = dead.includes('Arya Stark')console.log(isAryaDead)// falseconst isJoffreyDead = dead.includes('Joffrey')console.log(isJoffreyDead)// trueconst isJohnDead = dead.includes('Jon Snow', 1)console.log(isJohnDead)// false
          const dead = ['Jon Snow', 'Joffrey', 'Ned Stark', 'Night King']
const isAryaDead = dead.includes('Arya Stark')
console.log(isAryaDead)
// false

const isJoffreyDead = dead.includes('Joffrey')
console.log(isJoffreyDead)
// true

const isJohnDead = dead.includes('Jon Snow', 1)
console.log(isJohnDead)
// false

String:

        
          
          const text =  'Look, it’s nearby our panda. We are running with you as if from a cheetah.'console.log(text.includes('panda'))// trueconsole.log(text.includes('Monkey'))// false// The search is case-sensitiveconsole.log(text.includes('Panda'))// false
          const text =
  'Look, it’s nearby our panda. We are running with you as if from a cheetah.'

console.log(text.includes('panda'))
// true

console.log(text.includes('Monkey'))
// false

// The search is case-sensitive
console.log(text.includes('Panda'))
// false

In practice

Advice 1

🛠 Use the method when you need to ensure that the object is in the array. For example, to avoid adding the same value twice.

Open demo in the new window

🛠 Be careful when passing objects to includes(). If two objects look identical, it doesn't necessarily mean they are the same object because objects are stored by reference.

        
          
          const phoneContacts = [  { name: 'Ivan', lastName: 'Taranov' },  { name: 'Igor', lastName: 'Ivanov' },  { name: 'Mom', lastName: '' },]console.log(phoneContacts.includes(  { name: 'Mom', lastName: '' }))// false
          const phoneContacts = [
  { name: 'Ivan', lastName: 'Taranov' },
  { name: 'Igor', lastName: 'Ivanov' },
  { name: 'Mom', lastName: '' },
]

console.log(phoneContacts.includes(
  { name: 'Mom', lastName: '' }
))
// false

Here console.log() will output false, as we created a new object, even though it looks the same as the one in the array.

Briefly

Example

Features of using the second argument

In practice

Advice 1

Read also

.findIndex()

Set

Working with Forms

`.findIndex()`

`Set`