how to check is array in typescript code example

Example 1: javascript check if is array

var colors=["red","green","blue"];

if(Array.isArray(colors)){
    //colors is an array
}

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");
}