javascript - parseInt doesn't work - Stack Overflow

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in my current source code textbox value is 1. when I try alert(isNaN(obj.text()) it returns false that is expected but after parseInt when I write alert(a); it returns NaN

minus.click(function () {
     var a = 1; if (!isNaN(obj.text())) a = parseInt(obj.text()); 
     if (a > 1) a -= 1; obj.text(a);
});

what is the problem?

Edit: this is the full code:

<input type="text" class="basket-txt" value="1" />


jQuery.fn.basket = function (options) {
    var defaults = {
    }
    options = jQuery.extend(defaults, options);
    this.each(function () {
        var $this = $(this);
        $this.height(32).css({ 'line-height': '32px', 'font-weight': 'bold', 'width':'40px', 'text-align':'center', });
        var tbl = $('<table border="0" style="border-spacing:0px;float:left;">').appendTo($this.parent());
        var tr1 = $('<tr>').appendTo(tbl);
        var plus = $('<div class="basket-plus">');
        $('<td>').append(plus).appendTo(tr1);
        $('<td>').append($this).appendTo(tr1);
        var minus = $('<div class="basket-minus">');
        $('<td>').append(minus).appendTo(tr1);
        var tr2 = $('<tr>').appendTo(tbl);
        $('<td>').appendTo(tr2);
        $('<td>').appendTo(tr2).append($('<div>').addClass('add-to-basket'));
        $('<td>').appendTo(tr2);
        $this.keypress(function (e) { if (e.which < 48 || e.which > 57) e.preventDefault(); });
        minus.click(function () {

            var a = 1; if (!isNaN($this.text())) a = parseInt($this.text()); 
            if (a > 1) a -= 1; $this.text(a);
        });
        plus.click(function () {
            var a = 1; if (!isNaN($this.text())) a = parseInt($this.text());
            if (a < 1000000) a += 1; $this.text(a);
        });
    });
}

actually I knew I could correct the code and it would work my concern was to understand why isNaN returns false but parseInt returns NaN

in my current source code textbox value is 1. when I try alert(isNaN(obj.text()) it returns false that is expected but after parseInt when I write alert(a); it returns NaN

minus.click(function () {
     var a = 1; if (!isNaN(obj.text())) a = parseInt(obj.text()); 
     if (a > 1) a -= 1; obj.text(a);
});

what is the problem?

Edit: this is the full code:

<input type="text" class="basket-txt" value="1" />


jQuery.fn.basket = function (options) {
    var defaults = {
    }
    options = jQuery.extend(defaults, options);
    this.each(function () {
        var $this = $(this);
        $this.height(32).css({ 'line-height': '32px', 'font-weight': 'bold', 'width':'40px', 'text-align':'center', });
        var tbl = $('<table border="0" style="border-spacing:0px;float:left;">').appendTo($this.parent());
        var tr1 = $('<tr>').appendTo(tbl);
        var plus = $('<div class="basket-plus">');
        $('<td>').append(plus).appendTo(tr1);
        $('<td>').append($this).appendTo(tr1);
        var minus = $('<div class="basket-minus">');
        $('<td>').append(minus).appendTo(tr1);
        var tr2 = $('<tr>').appendTo(tbl);
        $('<td>').appendTo(tr2);
        $('<td>').appendTo(tr2).append($('<div>').addClass('add-to-basket'));
        $('<td>').appendTo(tr2);
        $this.keypress(function (e) { if (e.which < 48 || e.which > 57) e.preventDefault(); });
        minus.click(function () {

            var a = 1; if (!isNaN($this.text())) a = parseInt($this.text()); 
            if (a > 1) a -= 1; $this.text(a);
        });
        plus.click(function () {
            var a = 1; if (!isNaN($this.text())) a = parseInt($this.text());
            if (a < 1000000) a += 1; $this.text(a);
        });
    });
}

actually I knew I could correct the code and it would work my concern was to understand why isNaN returns false but parseInt returns NaN

• javascript
• jquery

Share Improve this question Follow edited Nov 17, 2013 at 16:02 Ashkan Mobayen Khiabani asked Nov 17, 2013 at 15:44 Ashkan Mobayen KhiabaniAshkan Mobayen Khiabani 34.2k3535 gold badges111111 silver badges184184 bronze badges 11

• 3 What exactly is the string value of obj.text()? Is it really just "1" or are there other characters? – Pointy Commented Nov 17, 2013 at 15:45
• I pasted the full code – Ashkan Mobayen Khiabani Commented Nov 17, 2013 at 15:46
• 1 (a side note: whenever you parseInt, add the radix: parseInt(str, 10), older JavaScript will surprise you otherwise) – Eric Commented Nov 17, 2013 at 15:48
• 1 @AshkanMobayenKhiabani you're making an incorrect assumption about what the isNaN() function does. – Pointy Commented Nov 17, 2013 at 15:51
• 1 No, isNaN will return false for "" which makes your code think it's a number but it isn't. You should re-write your code. Use obj.val() – Joe Simmons Commented Nov 17, 2013 at 15:58

 |  Show 6 more ments

4 Answers 4

Sorted by: Reset to default 5

The jQuery text() method will take all the descendent text nodes of an element and bine them into a single string.

An input element can't have descendant nodes of any kind. Its current value is exposed via the value property, which you can read with the val() method in jQuery.

You shouldn't use parseInt without a radix, especially with free form input. You might get octal or hex data instead of a decimal.

parseInt($this.val(), 10)

You get the value of an <input> with .val(), not .text().

The isNaN() function returns false for isNaN(""). Why? Because when "" (the empty string) is converted to a number, it's 0. Pass a non-number to isNaN() and the first thing it does is coerce the value into a number.

It's kind-of pointless to try isNaN() before parseInt() anyway, since parseInt() will tell you when it can't parse a nice-looking integer. Note however that parseInt() doesn't care if there's garbage at the end of the input.

If you want to convert a string to a number when it's a valid string representation of a number, and NaN when it isn't, you can use

var myNumber = +myString;

That'll accept numbers with fractional parts and exponents too, so you'd have to either truncate that to just an integer or check to see if it is one:

var myNumber = +myString;
if (isNaN(myNumber))
  // not a valid number
else if (myNumber !== Math.floor(myNumber))
  // not an integer
else
  // yaay!

minus.click(function () {
    // let's parse the integer first
     var num = parseInt( obj.val(), 10 );

     // then later, we can check if it's NaN
     if ( !isNaN(num) && num > 1 ) {
        num -= 1;
        obj.val(num);
     }
});

---

actually I knew I could correct the code and it would work my concern was to understand why isNaN returns false but parseInt returns NaN

isNaN doesn't work the way it should. There is type coercion going on.
isNaN will convert the value to a number first. An empty string will be converted to a 0

Number("") === 0; // true

0 is obviously not NaN, so it returns false.

parseInt doesn't do type coercion, it parses the value differently.

Check this question and this other question for reference.

parseInt returns NaN when the first non-whitespace character cannot be converted to a number.

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