Check if a value is in an Array in JavaScript

Background

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Given an array of strings, we want to know if a particular string value is in that array. Here we’ll use the Array object’s .indexOf function.

Software Environment

Any modern web browser

JavaScript Codes

var userIds = ['123ABC', '456DEF', '789GHI', '011JKL'];
if(userIds.indexOf('456DEF') > -1) 
{
    // Value is in the array
}

Sometimes, we retrieve arrays from other codes. We may check first if the array is truly an Array or is not undefined.

var userIds = service.getResponseDataFromServer();
if(userIds && Array.isArray(userIds)) 
{
    if(userIds.indexOf('456DEF') > -1) {
        // Value is in the array
    }
}