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 so         


        

Answer 1

function isEmpty(variable) {
  const type = typeof variable
  if (variable === null) return true
  if (type === 'undefined') return true
  if (type === 'boolean') return false
  if (type === 'string') return !variable
  if (type === 'number') return false
  if (Array.isArray(variable)) return !variable.length
  if (type === 'object') return !Object.keys(variable).length
  return !variable
}

Answer 2

Here my simplest solution.

Inspired by PHP empty function

function empty(n){
	return !(!!n ? typeof n === 'object' ? Array.isArray(n) ? !!n.length : !!Object.keys(n).length : true : false);
}

//with number
console.log(empty(0));        //true
console.log(empty(10));       //false

//with object
console.log(empty({}));       //true
console.log(empty({a:'a'}));  //false

//with array
console.log(empty([]));       //true
console.log(empty([1,2]));    //false

//with string
console.log(empty(''));       //true
console.log(empty('a'));      //false

Answer 3

Check for undefined:

if (typeof response.photo == "undefined")
{
    // do something
}

This would do the equivelant of vb's IsEmpty. If myvar contains any value, even null, empty string, or 0, it is not "empty".

To check if a variable or property exists, eg it's been declared, though it may be not have been defined, you can use the in operator.

if ("photo" in response)
{
    // do something
}

Answer 4

See http://underscorejs.org/#isEmpty

isEmpty_.isEmpty(object) Returns true if an enumerable object contains no values (no enumerable own-properties). For strings and array-like objects _.isEmpty checks if the length property is 0.

Answer 5

Here's a simpler(short) solution to check for empty variables. This function checks if a variable is empty. The variable provided may contain mixed values (null, undefined, array, object, string, integer, function).

function empty(mixed_var) {
 if (!mixed_var || mixed_var == '0') {
  return true;
 }
 if (typeof mixed_var == 'object') {
  for (var k in mixed_var) {
   return false;
  }
  return true;
 }
 return false;
}

//   example 1: empty(null);
//   returns 1: true

//   example 2: empty(undefined);
//   returns 2: true

//   example 3: empty([]);
//   returns 3: true

//   example 4: empty({});
//   returns 4: true

//   example 5: empty(0);
//   returns 5: true

//   example 6: empty('0');
//   returns 6: true

//   example 7: empty(function(){});
//   returns 7: false

Answer 6

if (myVar == undefined)

will work to see if the var is declared but not initalized.