Finding

After ES 2017

const myArray = ['Mon', 'Tue', 'Wed'];  
arrayContains(myArray, 'Tue');  // true  

function arrayContains(theArray, searchValue) { 
   return theArray.includes(searchValue); 
} 

Before ES 2017

const myArray = ['Mon', 'Tue', 'Wed'];  
arrayContains(myArray, 'Tue');  // true  

function displayDay(theArray, searchValue) { 
   return theArray.indexOf(searchValue) > -1; 
} 

indexOf

lastIndexOf

find

findIndex