无法弄清楚公式有什么问题

Question

var johnHeight = prompt('Enter the height');

var johnAge =prompt('Enter the age');

var ranaHeight = prompt('Enter the height');

var ranaAge =prompt('Enter the age');   

var johnScore = johnHeight + 5 * johnAge;

var win = document.getElementById('winner');

if (johnScore > ranaScore) {

        win.innerHTML = 'John is the winner with ' + johnScore + ' points';

}

else if (johnScore < ranaScore) {

    win.innerHTML = 'Rana is the winner with ' + ranaScore + ' points';
}

else if (johnScore == ranaScore) {

    win.innerHTML = 'It\'s a draw';
}

When I try to run the code, everything works fine but the formula ie JohnScore or ranaScore doesn't calculate correct values. when I remove the prompt and give those variables a predefined values, it works fine.. can someone solve please.

Answer 1

You don't have a variable set up for ranaScore, and for the johnScore variable if you mean to add 5 to his height and then multiply by age which means it needs to be:

var johnScore = (johnHeight + 5) * johnAge;

if that's not what you need you may try:

var johnScore = johnHeight + (5 * johnAge);

Answer 2

The value from prompt is coming as string. So to get the right calculation you need to convert that to number. Notice + before prompt. Also you need to define ranaScore .

So if johnHeight is "10" and johnAge is "5", let's look how this was being evaluated by javascript:

var johnScore = johnHeight + 5 * johnAge;

johnScore = "10" + 5* "5" which is "10" + "25" which is "1025".

 var johnHeight = +prompt('Enter the height'); var johnAge = +prompt('Enter the age'); var ranaHeight = +prompt('Enter the height'); var ranaAge = +prompt('Enter the age'); var johnScore = johnHeight + 5 * johnAge; var ranaScore = ranaHeight + 5 * ranaAge; var win = document.getElementById('winner'); if (johnScore > ranaScore) { win.innerHTML = 'John is the winner with ' + johnScore + ' points'; } else if (johnScore < ranaScore) { win.innerHTML = 'Rana is the winner with ' + ranaScore + ' points'; } else if (johnScore == ranaScore) { win.innerHTML = 'It\\'sa draw'; } 

 <div id="winner"></div> 

Answer 3

Looks like your variable ranaScore has not been defined, so you need this line.

            var ranaScore = rannaHeight + 5 * rannaAge;

Although in real life scenario you will need to build your JS function to receives arguments instead of using static variables eg see very basic example below.

            function comparevalues(arg1,arg2){
                if (arg1 > arg2) {
                    win.innerHTML = arg1 + 'is greater than ' + arg2; //arg 1 wins
                }
                else if (arg1 < arg2) {
                    win.innerHTML = arg2 + 'is greater '  + arg1; //arg 2 wins
                }
                else {
                    win.innerHTML = arg2 + 'is equal to '  + arg1; //draw
                }
            }
            comparevalues(4,5)

Answer 4

Always prompt returns string type , convert it into number using ParseInt method. var johnHeight=parseInt(prompt('Enter the height'));