javascript comparison operator not evaluating user input correctly

Question

Disclaimer: I'm an idiot.

This is extremely simple. I must be doing something very basic wrong, but I've spent a ton of time trying to figure it out, and I'm stumped.

For reference, The Entire Code:

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Not comparing correctly</title>
</head>
<script>

//This is the main function. It creates a new game and plays it.
function playTheGame() {
    "use strict";
    //create the game object
    var currentGame = new game();
    //play the game
    currentGame.play(document.getElementById("eCurrentStake").value, document.getElementById("eGoalAmount").value);
}

// This is the game object.
function game(){
    //properties
    this.goalAmount = 0;
    this.currentStake = 0;

    //Play method Plays the game and stores the results in properties
    this.play=play;
    function play(currentStake,goalAmount){
        //set the relevant properties to values passed to the object
        this.goalAmount = goalAmount;
        this.currentStake = currentStake;
        alert(this.currentStake+" < "+this.goalAmount+" :"+(this.currentStake < this.goalAmount));
    };
}
</script>

<body>
    Enter Current Stake: <input type="text" id="eCurrentStake"></input><br>
    Enter Goal Amount: <input type="text" id="eGoalAmount"></input><br>

    <button type="button" onclick="playTheGame()">Let's Play!</button>
</body>
</html>

The part of the code that's giving me trouble:

alert(this.currentStake+" < "+this.goalAmount+" :"+(this.currentStake < this.goalAmount));

When I put 9 and 10 into the input text fields, I get a, "false," output. but 10 and 50 does return true. In short: the result is unpredictable. I think it might be evaluating as a string, but when I researched it, all I can find is that Javascript has dynamic data types and will compare variables as numbers if they are numbers. ie :

http://www.w3schools.com/js/js_datatypes.asp

So, where am I going wrong?

@SLaks I've never done work with javascript so it's an entire field i need to learn about <.< — progrenhard
– progrenhard, Commented Sep 17, 2013 at 18:32
Thanks everyone for all the responses! They're very much appreciated! Now, I'm off to research the difference between parseInt() vs. Number() — jgrant
– jgrant, Commented Sep 17, 2013 at 18:51

Rusty Bailey · Accepted Answer · 2013-09-17 18:33:14Z

2

May need to use parseInt to convert arguments into numbers:

this.goalAmount = parseInt(goalAmount);
this.currentStake = parseInt(currentStake);

answered Sep 17, 2013 at 18:33

Rusty Bailey

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Comments

Billy Moon · Accepted Answer · 2013-09-17 18:31:20Z

0

wrap the things you want to compare with parseInt to convert them to numbers - otherwise they will be compared as strings

answered Sep 17, 2013 at 18:31

Billy Moon

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Comments

Jaime · Accepted Answer · 2013-09-17 18:31:40Z

0

You can use the number function: http://www.w3schools.com/jsref/jsref_number.asp

answered Sep 17, 2013 at 18:31

Jaime

1

2 Comments

SLaks Over a year ago

w3fools.com developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…

jgrant Over a year ago

For some reason, when I tried this, it fixed the issue but created an issue when I tried dividing the currentStake by the goalAmount to get a percentage. There was no error, but it was returning unexpected results. When I used the parseInt() function all was copacetic.

user2625787 · Accepted Answer · 2013-09-17 18:32:16Z

0

Input values are indeed strings, as you suspect. Cast them to numbers:

this.goalAmount = Number(goalAmount);
this.currentStake = Number(currentStake);

It boils down to this:

"9" < "10" // false
Number("9") < Number("10") // true

answered Sep 17, 2013 at 18:32

user2625787

Comments

Tony · Accepted Answer · 2013-09-17 18:33:35Z

0

change this line

currentGame.play(parseInt(document.getElementById("eCurrentStake").value), parseInt(document.getElementById("eGoalAmount").value));

answered Sep 17, 2013 at 18:33

Tony

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