Checking if multiple variables is not null, undefined or empty in an efficient way

If IE support matter to you (IE9+), you could use the following solution.

You could use Array.prototype.some(). In a nutshell this array method will return true if any of the elements in the array meet a certain condition. This condition will be el == null this will work because undefined == null and null == null both resolve in true

See this stackoverflow post for more information

Which equals operator (== vs ===) should be used in JavaScript comparisons?

Array.prototype.some() browser support (93% time of writing) here

var a = 5;
var b = null;
var c = undefined;

if ( [a,b,c].some(el => el == null) ) {          
  console.log("You f*d up")
}

Or you could use Array.prototype.includes()

See support (93% time of writing) here here

var a = 5;
var b = null;
var c = undefined;
   
 if ( [a,b,c].includes(undefined) || [a,b,c].includes(null) ) {          
   console.log("You f*d up")
 }

If you want good browser support and you don't mind an external library, use lodash.

var a = 5;
var b = null;
var c = undefined;

if ( _.some([a,b,c], el => _.isNil(el)) ) {
  console.log("You f*d up")
}

<script src="https://cdn.jsdelivr.net/lodash/4.17.4/lodash.min.js"></script>

If your variables are containing some values that are truthy, like a string, and that is considered positive in your condition, then you could simply check using Array.prototype.every()...

if (![var1, var2, var3].every(Boolean)) {
     throw new exc;
}

Which will check to ensure every variable has a truthy value.

I assume you are checking for truthy values? If so, you can just do:

variable && variable2 && variable3

See JavaScript: What is the difference between if (!x) and if (x == null)?

!variable will be true for all falsy values so you only have to

if(variable1 && variable2 && variable3 && ...)

Long hand -

 if (var1 !== null || var1 !== undefined || var1 !== '') {
   let var2 = var1;
 }

Short hand -

 const var2 = var1  || '';

let variable null;
let variable2 undefined;
let variable3 'string';
let variable4 '';
let variable5 true;
let variable6 false;
let variable7 0;
let variable8 1;

Validating multiple values using the filter function. One could expect this example to return true as the count would be 5 for (variable, variable2, variable4, variable6, variable7)

if([variable, variable2, variable3, variable4, variable5, variable6, variable7, variable8]
  .filter(q=>!q).length > 0) {
   //take action
}