Adding an integer to a JavaScript variable

Question

I have a variable declared here:

var quizScore = 0;

And I want to add a number to it each time the correctAnswer() function runs:

function correctAnswer(){
  quizScore+1;
    console.log ( 'correct answer selected: quizscore = ' + quizScore );
}

I added a console log for debugging. It works, so the function is being called, but it is not adding the score. Do I need to parse this to an integer? I can't work out what the +1 needs to be to work correctly.

You can go here and you will see that clicking "Lightning Bolt" for question 1 shows "correct answer" in the console, but doesn't add to the score variable.

it should be quizScore = quizScore + 1. You're not assigning anything when you add. — George Stocker
– George Stocker, Commented Mar 14, 2014 at 17:57
well it seems like you are new to js and posting questions along the way you are working on this quiz app, i suggest making a jsfiddle.net and linking to it from your questions.. — T J
– T J, Commented Mar 14, 2014 at 18:01
Not sure why this is being downvoted. A valid question with sufficient information and background. — theGreenCabbage
– theGreenCabbage, Commented Mar 14, 2014 at 19:28

George Sofianos · Accepted Answer · 2014-03-14 18:01:50Z

3

Do it like this:

function correctAnswer(){
    console.log ( 'correct answer selected: quizscore = ' + (++quizScore) );
}

You just need to assign the +1 to quizScore variable. This may be the fastest way to add 1 and display it in one line

answered Mar 14, 2014 at 18:01

George Sofianos

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Comments

user229044 · Accepted Answer · 2014-03-14 17:57:42Z

1

You're adding one to whatever value is in quizScore, and doing nothing with the result.

You need quizScore = quizScore + 1.

answered Mar 14, 2014 at 17:57

user229044♦

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1 Comment

T J Over a year ago

or simply quizScore++;

nanobash · Accepted Answer · 2014-03-14 18:14:17Z

1

Keep quizscore as global variable. And secondly change the line no.1 of your correctAnswer() function to

quizScore = quizScore + 1;

edited Mar 14, 2014 at 18:14

nanobash

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answered Mar 14, 2014 at 18:00

Bhavesh Munot

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Comments

nanobash · Accepted Answer · 2014-03-14 18:16:55Z

1

You can use self-memorizing function not to pollute global environment with variables like so:

function correctAnswer() {
    correctAnswer.quizScore = (correctAnswer.quizScore || 0) + 1;
    console.log("QuizScore : " + correctAnswer.quizScore);
}

for (var i = 0; i < 10; i++) {
    correctAnswer(); // output 1 2 3 4 5 6 7 8 9 10
}

edited Mar 14, 2014 at 18:16

answered Mar 14, 2014 at 18:06

nanobash

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1 Comment

user229044 Over a year ago

Just correctAnswer.quizScore = (correctAnswer.quizScore || 0) + 1 would suffice

Dissident Rage · Accepted Answer · 2014-03-14 18:35:11Z

Right now, when you do this:

quizscore+1;

You add one to it but it doesn't assign the change to the variable. One reason for this is that sometimes you may want to add a number to the variable long enough to perform an operation but you don't want it to change.

// quiz score is left alone
var nextscore = quizscore + 1

Here are the different ways to actually assign it:

// temporarily adds 1 to quizscore, then saves it to quizscore
quizscore = quizscore + 1

// adds one to quizscore after it's used in an expression
quizscore++

// adds one to quizscore before it's used in an expression
++quizscore

So if you did something like this:

var nextscore = ++quizscore + 1;

You would both increment the current score and predict the next score.

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