var myVar=null; if(myVar === null){ //I am null; } if (typeof myVar === 'undefined'){ //myVar is undefined }
//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"); }