if in_array js code example

Example 1: js in_array

var a = [1, 2, 3];
a.includes(2); // true 
a.includes(4); // 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");
}