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

Empty check on a JSON's key depends on use-case. For a common use-case, we can test for following:

1. Not null
2. Not undefined
3. Not an empty String ''
4. Not an empty Object {} [] (Array is an Object)

Function:

function isEmpty(arg){
  return (
    arg == null || // Check for null or undefined
    arg.length === 0 || // Check for empty String (Bonus check for empty Array)
    (typeof arg === 'object' && Object.keys(arg).length === 0) // Check for empty Object or Array
  );
}

Return true for:

isEmpty(''); // Empty String
isEmpty(null); // null
isEmpty(); // undefined
isEmpty({}); // Empty Object
isEmpty([]); // Empty Array

Answer 2

It depends on what you mean by "empty". The most common pattern is to check to see if the variable is undefined. Many people also do a null check, for example:
if (myVariable === undefined || myVariable === null)...

or, in a shorter form:
if (myVariable || myVariable === null)...

Answer 3

just put the variable inside the if condition, if variable has any value it will return true else false.

if (response.photo){ // if you are checking for string use this if(response.photo == "") condition
 alert("Has Value");
}
else
{
 alert("No Value");
};

Answer 4

what am I missing if empty array... keyless object... falseness const isEmpty = o => Array.isArray(o) && !o.join('').length || typeof o === 'object' && !Object.keys(o).length || !(+value);

Answer 5

If you're looking for the equivalent of PHP's empty function, check this out:

function empty(mixed_var) {
  //   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({'aFunc' : function () { alert('humpty'); } });
  //   returns 5: false

  var undef, key, i, len;
  var emptyValues = [undef, null, false, 0, '', '0'];

  for (i = 0, len = emptyValues.length; i < len; i++) {
    if (mixed_var === emptyValues[i]) {
      return true;
    }
  }

  if (typeof mixed_var === 'object') {
    for (key in mixed_var) {
      // TODO: should we check for own properties only?
      //if (mixed_var.hasOwnProperty(key)) {
      return false;
      //}
    }
    return true;
  }

  return false;
}

http://phpjs.org/functions/empty:392

Answer 6

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 };