includes() JavaScript Array Method – How to Check If an Array Includes an Item
Whenever you use includes() on an array, the method does the following:
- It checks if the calling array includes the method’s first argument.
- It returns
true
if the array includes the argument. Otherwise, it returnsfalse
.
Syntax of the includes()
Method
includes()
accepts two arguments. Here is the syntax:
callingArray.includes(valueToFind, startIndex);
Argument 1: valueToFind
A valueToFind
is the first argument accepted by the includes()
method. It defines the value you wish to find in the calling array.
Example 1: Check if a given array includes "Tuesday"
["Sunday", "Tuesday", "Friday"].includes("Tuesday");
// The invocation above will return: true
Example 2: Check if a given array includes "SunDay"
["Sunday", "Tuesday", "Friday"].includes("SunDay");
// The invocation above will return: false
The snippet above returned false
because the includes()
method is case-sensitive.
Example 3: Check if a given array includes 5
[1, 3, 5, 7].includes(5);
// The invocation above will return: true
Argument 2: startIndex
The startIndex
argument is optional. It specifies the index position where you want the computer to start searching for the valueToFind
argument.
Example 1: From the 3rd index position, check if a given array includes "Tuesday"
const daysOfWeek = [ "Sunday", "Tuesday", "Thursday", "Friday", "Tuesday", "Sunday", "Tuesday", "Friday",];
daysOfWeek.includes("Tuesday", 3);
// The invocation above will return: true
Example 2: From the 1st index position, check if a given array includes "Sunday"
const daysOfWeek = [ "Sunday", "Tuesday", "Friday", "Monday", "Tuesday", "Friday",];
daysOfWeek.includes("Sunday", 1);
// The invocation above will return: false