Checking something isEmpty in Javascript?

Question

How can I check if a variable is empty in Javascript? Sorry for the stupid question, but I'm a newbie in Javascript!

if(response.photo) is empty {     do something else {     do something else } 

response.photo was from JSON, and it could be empty sometimes, empty data cells! I want to check if it's empty.

Answer 1

If you're testing for an empty string:

if(myVar === ''){ // do stuff }; 

If you're checking for a variable that has been declared, but not defined:

if(myVar === null){ // do stuff }; 

If you're checking for a variable that may not be defined:

if(myVar === undefined){ // do stuff }; 

If you're checking both i.e, either variable is null or undefined:

if(myVar == null){ // do stuff }; 

Answer 2

This is a bigger question than you think. Variables can empty in a lot of ways. Kinda depends on what you need to know.

// quick and dirty will be true for '', null, undefined, 0, NaN and false. if (!x)   // test for null OR undefined if (x == null)    // test for undefined OR null  if (x == undefined)   // test for undefined if (x === undefined)  // or safer test for undefined since the variable undefined can be set causing tests against it to fail. if (typeof x == 'undefined')   // test for empty string if (x === '')   // if you know its an array if (x.length == 0)   // or if (!x.length)  // BONUS test for empty object var empty = true, fld; for (fld in x) {   empty = false;   break; }