can you explain how works letters[pass[i]] = (letters[pass[i]] || 0) 1? I have debugged the function, but can't catch the logic.

    function scorePassword(pass) {
            var score = 0;
            if (!pass)
                return score;
        
            // award every unique letter until 5 repetitions
            var letters = new Object();
            for (var i=0; i<pass.length; i  ) {
                **letters[pass[i]] = (letters[pass[i]] || 0)   1;**
                score  = 5.0 / letters[pass[i]];
            }
        
            // bonus points for mixing it up
            var variations = {
                digits: /\d/.test(pass),
                lower: /[a-z]/.test(pass),
                upper: /[A-Z]/.test(pass),
                nonWords: /\W/.test(pass),
            }
        
            var variationCount = 0;
            for (var check in variations) {
                variationCount  = (variations[check] == true) ? 1 : 0;
            }
            score  = (variationCount - 1) * 10;
        
            return parseInt(score);
}

CodePudding user response：

This line adds letters from pass to the letters object as keys and it's number of occurs in the value.

So, for example, for pass = "aabbc" you'll have letters equal to

{
  "a":2,
  "b":2,
  "c":1
}

The operator on the right ((letters[pass[i]] || 0) 1) can be splitted to two: letters[pass[i]] || 0 checks if letters has key of value pass[i], if so the expression will have it's value, if not then we will get value after || - in this case 0. To value of this expression we add always 1.

Also, we could convert this one line to something like this:

if(letters[pass[i]]) {
  letters[pass[i]]  ;
} else {
  letters[pass[i]] = 1;
}

About the || operator in value assignment you can read more for example here

CodePudding user response：

Let's start on the right, like the JavaScript engine does. :-)

(letters[pass[i]] || 0)   1

That:

• Starts with pass[i] which gets the letter for index i from pass (which appears to be a string)
• Then tries to get the value for a property with that name from letters (letters[pass[i]]). It will either get a number that it's put there before or, if there is no property for that letter (yet), it'll get the value undefined.
• It uses that value (a number or undefined) with (the value) || 0. The || operator works fairly specially in JavaScript: It evaluates its left-hand operand and, if that value is truthy, takes that value as its result; otherwise, it evaluates its right-hand operand and takes that value as its result. undefined is a falsy value, so undefined || 0 is 0. This is to handle the first time a letter is seen.
• It adds 1 to the result it got from ||.

Basically, that's adding one to the value of the property for the letter on letters, allowing for never having seen that letter before via ||.

Then it stores the result back to the property.