js check if array includes code example

Example 1: js test if array

if(Array.isArray(myVarToTest)) {
	// myVatToTest is an array
} else {
	// myVarToTest is not an array
}

Example 2: js array includes

[1, 2, 3].includes(2);     // true
[1, 2, 3].includes(4);     // false
[1, 2, 3].includes(3, 3);  // false
[1, 2, 3].includes(3, -1); // true
[1, 2, NaN].includes(NaN); // true

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");
}