check value is array or not in javascript code example

Example 1: if object is array javascript

Array.isArray(object);

Example 2: in javascript check is is an array or not

Array.isArray(yourItem)

Example 3: 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");
}