Proper way of multiple variable assignment in Javascript [duplicate]

Question

(function(){
    var b1 = b2 = b3 = b4 = 100;
})();

console.log(b1); //100
console.log(b2); //100
console.log(b3); //100
console.log(b4); //100

Here assignment is right associative and hence 100 is assigned.

It is a bad practice. Better version is

(function(){
  'use strict';
   var b1 = 100,
   b2 = 100,
   b3 = 100,
   b4 = 100;
})();

Question: Is there any case where such wrong assignment

var b1 = b2 = b3 = b4 = 100; 

could be preferred or should it never be used?

Answer 1

It is not okay, since those 2 code examples are not identical. The first one equals to:

var b1;
b4 = 100;
b3 = b4;
b2 = b3;
b1 = b2;

So you only define b1 in the local scope, the b2..b4 are declared globally. Which means this MUST BE completely avoided.

I also highly doubt console.log(b1); outputs 100 as per your example.

(function(){
    var b1 = b2 = b3 = b4 = 100;
})();

console.log(b1); //100 <-- this is not true
console.log(b2); //100
console.log(b3); //100
console.log(b4); //100

From the other hand - for already declared variables - initialization or assignment using

// we assume a, b and c have been declared already
a = b = c = 100;

is a subject of your project/team conventions. From technical perspective it's fine to use it.