javascript return true if element in array code example

Example 1: javascript check if any value in array is true

let boolArray1 = [true, false, false]
let boolArray2 = [false, false, false]

boolArray1.some(x => x);  // true
boolArray2.some(x => x);  // false

// Example of using a function to evaluate array
let numberArray = [1, 2, 3, 4, 5];
let oddNumbers = [1, 3, 5, 7, 9];

// checks whether an element is even
const even = (element) => element % 2 === 0;

numberArray.some(even);  // true
oddNumbers.some(even);   // false

Example 2: javascript check if in array

var extensions = ["image/jpeg","image/png","image/gif"];          
if(extensions.indexOf("myfiletype") === -1){
	alert("Image must be .png, .jpg or .gif");
}