check empty and null in javascript code example

Example 1: javascript check if null

if (variable === null) { //Executes only if variable is null but not undefined
  //Code here
}

if (variable == null) { //Executes if variable is null OR undefined
  //Code here
}

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");
}