eugenedrvnk

1. == и === (одинаково)
   
2. &&
   
3. ||
   

var root = 
  ( typeof self == 'object' && self.self === self && self )  ||
  ( typeof global == 'object' && global.global === global && global )  ||
  ( this );

var root = 
  ( (typeof self == 'object') && (self.self === self) && (self) )  ||
  ( (typeof global == 'object') && (global.global === global) && (global) )  ||
  ( this );

• self в Worker'ах;
  
• global определена в nodejs;
  
• this в прочих.
  

const root = (() => {
  if (typeof self == 'object' && self.self === self) {
    return self
  } 
  if (typeof global == 'object' && global.global === global ) {
    return global
  } 
   return this;
 }
})();

function* permutatins(s) {
    if (s.length > 1)
        for (let i = 0; i < s.length; i++)
            for (let t of permutatins(s.slice(0, i) + s.slice(i + 1)))
                yield s.charAt(i) + t;
    else yield s;
}

for (let s of permutatins('941'))
    console.log(s);