if(arrayName[index]==""){
     // do stuff
}

if (index < array.length) {
  // do stuff
}

if (typeof array[index] !== 'undefined') {

if (typeof array[index] !== 'undefined' && array[index] !== null) {

if (array[index] != null) {
  // The == and != operator consider null equal to only null or undefined

if(arrayName.length > 0){
    //or **if(arrayName.length)**
    //this array is not empty
}else{
   //this array is empty
}

if(!arrayName[index]){
     // do stuff
}

if(array && array.length){
   // not empty
} else {
   // empty
}

Objects.keys(__array__).length

if(arrayName.length > index && arrayName[index] !== null) {
    //arrayName[index] has a value
}

if(typeof arr ==='object' && arr instanceof Array ){
   if(!arr.length){
      println 'empty'
   }else{
      printn 'not Empty'
   }

}else{
   println 'Null'
}

if(!arr.clean().length){return 'is null'}

Array.prototype.clean=function(){return this.filter(function(e){return (typeof  e !=='undefined')&&(e!= null)&&(e!='')})}

function isEmptyEl(array, i) {
   return !(array[i]);
}

if (isEmptyEl(arrayName, indexVal)) {
   console.log('arrayName[' + indexVal + '] is empty');
}

Uncaught ReferenceError: arrayName is not defined
    at <anonymous>:2:15
    at Object.InjectedScript._evaluateOn (<anonymous>:895:140)
    at Object.InjectedScript._evaluateAndWrap (<anonymous>:828:34)
    at Object.InjectedScript.evaluate (<anonymous>:694:21)

index in array;
array.hasOwnProperty(index);

if (array[index] != null)

if(_.has(req,'documents')){
      if (req.documents.length)
      _.forEach(req.documents, function(document){
        records.push(document);
      });
} else {
}

if(typeof arrayName[index]==="undefined"){
     //the index is not in the array
}

if(typeof arrayName[index]==="undefined"||arrayName[index]){
     //the index is not defined or the value an empty value
}

render: function (data, type, full) {
    if (full.properties.length !== 0) {
        // do stuff
    }
}

var pets = ['dog', undefined, 'cat', null];

console.log(_.isEmpty(pets[1])); // true
console.log(_.isEmpty(pets[3])); // true
console.log(_.isEmpty(pets[4])); // false

_.map( pets, (pet, index) => { console.log(index + ': ' + _.isEmpty(pet) ) });