字符串计算的小数

Question

I have this javascript code for a quiz programme but i can't figure out how to return the calculation result of the last context line with only 1 decimal. Any suggestions ?

EndQuiz=function(){
                  canvas.removeEventListener('click',ProcessClick,false);
                  context.drawImage(quizbg, 0,0,550,90,0,0,550,400);
                  context.font = "20pt Georgia,Arial";
                  context.fillText("Thanks for finishing. ",20,80);
          context.fillText("This is how good you were:",20,120);
                  context.font = "16pt Georgia,Calibri,Arial";
                  context.fillText("Correct answers: "+String(rightanswers)+" of "+String(rightanswers+wronganswers),20,180);

          context.fillText("Correct: "+String(rightanswers/(wronganswers+rightanswers)*100)+"%",20,240);1

Answer 1

Directly from W3schools:

Convert a number into a string, keeping only two decimals:

var num = 5.56789;
var n=num.toFixed(2);

The result of n will be:

5.57

the rest is left as an exercise for the reader :-)

Answer 2

Here is a functional function that can truncate decimals:

truncateDecimal = function(decimal, numDecimals) {
    var decString = ""+decimal;
    var dotIndex = decString.indexOf(".");
    var numChars = dotIndex + 1 + numDecimals;
    return parseFloat(decString.substring(0, numChars));
}

Now truncateDecimal(3010101.234, 1); returns 3010101.2 .