In javascript, to check a variable contain a valid data or not, we can use the below code.

var value;
if(value){
  // do something
}

If the variable doesn't contain a valid value it may have following 6 type of content.
This checking will valid if the variable is already defined.

null
undefined
NaN
empty string ("")
0
false

if the value is an array you need to check the length of value is not equal to zero.
(value.length != 0).


The safest way to check the variable is valid.
if (typeof value != 'undefined' && value) {
  // Do something
}