Javascript Common Mistakes

1. Javascript Common Mistakes Dongsu Jang <iolothebard at gmail.com> http://blog.iolo.pe.kr

2. Unaware of:Async! Async! Async! var result1, result2, result3; $.ajax(..., success: function(data) { result1 = data; }); $.ajax(..., success: function(data) { result2 = data; }); result3 = result1 + result2; But, don’t do that: “async: false”

3. Unaware of:this “this” is not the “this” function test(name, button) { this.name = name; button.onclick= function(event) { alert('hello, ' + this.name); }; }

4. Unaware of:“not of not” is not the not of “not” function test(foo) { alert(typeof(foo)); alert(foo); if (foo) { alert('foo'); } if (!foo) { alert(‘!foo'); } if (!!foo) { alert('!!foo'); } }

5. Misunderstaning0, null, false, undefined, NaN and “” function test(foo) { alert(typeof(foo)); alert(foo); if (foo) { alert('foo'); } if (foo == null) { alert('foo == null'); } if (foo === null) { alert('foo === null'); } }

6. Trying todeclaring block scope “var”s function test() { var foo = -1; for (varfoo = 0; foo < 10; foo++) { … } alert(foo); }

7. Trying tooverload a function function test(foo) { alert('one arg'); } function test(foo, bar) { alert('two args'); } function test() { for (var i = 0; i < arguments.length; i++) { alert(arguments[i]); } }

8. Using escape() instead of encodeURIComponent(), encodeURI() Checkout http://xkr.us/articles/javascript/encode-compare/ Rule of thumb! use encodeURIComponent() use encodeURI() only if you know what it is forget escape()

9. Unaware ofstring is not array-of-characters var str = “hello”; alert(str.charAt(2)); alert(str[2]); Similarly, NodeList is not array-of-Nodestoo!

10. Missing“radix” for parseInt() var sum = parseInt(num1.value) + parseInt(num2.value); alert(sum); parseInt('1234'); parseInt('01234'); parseInt('1234', 8); parseInt('01234', 10);

11. Sorry…it’s a comma… just a trailing comma… var test = { 1, 2, 3, }; out.print(“{“); for (int val: values) { out.print(i); out.print(“,”); } out.print(“}”);

12. Using Vanilla JavaScript Checkout http://en.wikipedia.org/wiki/Comparison_of_JavaScript_frameworks http://jquery.com/ http://prototypejs.org/ http://dojotoolkit.org/ and so on…

13. Testing in one browserand expecting it to work in another Checkout http://www.quirksmode.org/

14. Not using jslint Checkout http://jslint.com/

15. The most common mistake is“using JavaScript” Thanks you… ;)