how to check in array in javascript code example

Example 1: javascript array contains

var colors = ["red", "blue", "green"];
var hasRed = colors.includes("red"); //true
var hasYellow = colors.includes("yellow"); //false

Example 2: javascript test if it is an array

// If you want to test if a variable (object) is an instance of 
// an array. You can use the Array.isArray(varName) method
// this method takes one argument, the variable or object you want to test
// and returns true, if the argument is an array 
// or false, if the argument is not an array

if (Array.isArray(object)) {
	// is true
} else {
	// is false
}

Array.isArray([1, 2, 3, 4]); // Returns true
Array.isArray(4); // returns false
// this could be used for flattening an array of arrays

Example 3: how to check if item is in list js

var myList=["a", "b", "c"];
mylist.includes("d")//returns true or false

Example 4: 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");
}