Javascript function changing global variable (array)

Question

I am trying to make a Yahtzee game. I have a function to check if the dice rolled are a small straight.

var sortedDice = rollDice().sort(); // rollDice() generates an array with 5 random numbers

My function to determine if there is a small straight:

function isSmStraight(checkSmStraight){
    var smStraight = false;

    var i = 1;
    var j = 0;

    //will remove a die if there are duplicates
    while(i < checkSmStraight.length){
        if (checkSmStraight[i] == checkSmStraight[j]){
            i++;
        } else {
            j++;
            checkSmStraight[j] = checkSmStraight[i];
            i++;
        }//end if else
    }//end while loop that moves duplicates to last index of array
    checkSmStraight.pop();//removes last index of array

    if (isLgStraight(checkSmStraight) == true){
        smStraight = true;
    } else if (checkSmStraight.length == 4 && checkSmStraight[checkSmStraight.length-1] - checkSmStraight[0] == 3){
        smStraight = true;
    }//end if else if
    return smStraight;
}//end function isSmStraight()

I have copied sortedDice to another array, fourDice, that I can use to call isSmStraight(). I want just this function to use the four-index array, but it always messes with sortedDice, so the rest of the program uses the four-dice array. (This isn't the whole program, just the parts I thought are relevant. Also, the program is finished, I'm just trying to get the scoring functions right first).

You must define global var outside if your function, like var newvar = ""; function test() { newvar = "new text"; } — Eugen
– Eugen, Commented Dec 25, 2014 at 19:20
You're probably passing a reference, not a new array, use .slice() to create a copy. — adeneo
– adeneo, Commented Dec 25, 2014 at 19:22
Yes, the global variables are defined outside the function. Using .slice() worked perfectly. Thanks both for the quick responses. — Aaron Cannon
– Aaron Cannon, Commented Dec 25, 2014 at 19:37

Mayank Gupta · Accepted Answer · 2014-12-25 19:31:36Z

2

Arrays are by default, passed be reference in JavaScript. So if you're just doing something like var fourDice = sortedDice and then edit fourDice, sortedDice will also get edited Please also put the code where you're copying sortedDice to fourDice in the question.

answered Dec 25, 2014 at 19:31

Mayank Gupta

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1 Comment

Aaron Cannon Over a year ago

That's exactly what I was doint wrong. Using .slice() worked perfectly. Now I just need to figure out how to mark this as solved (new to the site).

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