check if field is empty javascript code example

Example 1: if input value is null do something

if(document.getElementById("question").value.length == 0)
{
    alert("empty")
}

Example 2: javascript check if empty

//check if string is undefined 
if (typeof myVar === 'undefined'){
  console.log("I am not defined");
}

//check if string is empty, null, or 0
var emptyString="";
if (emptyString) {
    console.log("im not empty");
}