'javascript tips'에 해당되는 글 1건

  1. 2008.02.20 JavaScript Tips

JavaScript Tips

ITWeb/개발일반 2008.02.20 17:48

 
Semicolon insertion
-When the compiler sees an error, it attempts to replace a nearby linefeed with a semicolon and try again.
-This should alarm you.
-It can mask errors.
-Always use the full, correct forms, including semicolons.
Comma
-Good: [1, 2, 3]
-Bad:  [1, 2, 3,]

 
Required block
-Good:
§if (a) {
§    b();
§}
-Bad:
§if (a) b();
== and !=
-Bad
§if (a == null) { ... }
-Good:
§if (a === null) { ... }
§if (!a) { ... }

 
Common subexpression removal
Loop invariant removal
for (var i = 0; i < divs.length; i += 1) {
    divs[i].style.color = "black";
    divs[i].style.border = thickness + 'px solid blue';
    divs[i].style.backgroundColor = "white";
}

----->
 
var border = thickness + 'px solid blue',
    nrDivs = divs.length;
for (var i = 0; i < nrDivs; i += 1) {
    var ds = divs[i].style;
    ds.color = "black";
    ds.border = border;
    ds.backgroundColor = "white";
}

 
Strings
-Concatenation with +
§Each operation allocates memory
foo = a + b;
-Concatenate with array.join('')
§The contents of an array are concatenated into a single string
-Comparison
§a) foo = a + b; vs b) foo = [a, b].join('');
a)  <  b)
§a) foo = 'a' + 'b'; vs b) foo = ['a', 'b'].join('');
a)  >  b)


 
-Place <script src> tags as close to the bottom of the body as possible. (Also, place CSS <link> as high in the head as possible.)
-Minify and gzip script files.
-Reduce the number of script files as much as possible.
<script></script>
<!--  // -->
§Hack for Mosaic and Navigator 1.0.
language=javascript
§Deprecated.
src=URL
§Highly recommended.
§Don't put code on pages.
type=text/javascript
§Ignored.

 
document.write
-Allows JavaScript to produce HTML text.
-Before onload: Inserts HTML text into the document.
-After onload: Uses HTML text to replace the current document.
-Not recommended.

 
name
-Identifies values in form data
-Identifies a window/frame
id
-Uniquely identifies an element


 
document.all
-Microsoft feature, rejected by W3C and most other browsers.
-It acts as a function or array for accessing elements by position, name, or id.
-Avoid it.


 
Manipulating elements
-Old
§if (my_image.complete) {
§    my_image.src = superurl;
§}
-New
§if (my_image.getAttribute('complete')) {
§    my_image.setAttribute('src', superurl);
§}


 
Element id 통한 접근
var oElement = null;
if ( document.getElementById ) {
oElement = document.getElementById(ID);
} else if ( document.layers ) {
oElement = document.layers[ID];
} else if ( document.all ) {
oElement = document.all[ID];
}


 
var oHttp = false;
var aMsxmlType = [
'MSXML2.XMLHTTP.5.0',
'MSXML2.XMLHTTP.4.0',
'MSXML2.XMLHTTP.3.0',
'MSXML2.XMLHTTP',
'Microsoft.XMLHTTP'
];
if ( window.XMLHttpRequest ) {
try {
oHttp = new XMLHttpRequest();
} catch(e) {
oHttp = false;
}
} else if ( window.ActiveXObject ) {
for ( i=0; i<this.aMsxmlType.length; i++ ) {
try {
oHttp = new ActiveXObject(this.aMsxmlType[i]);
if ( oHttp ) {
break;
}
} catch(e) {
oHttp = false;
}
}
}

 
JavaScritp XMLDOM
var oXmlDoc = null;
if ( window.ActiveXObject ) {
oXmlDoc = new ActiveXObject("Microsoft.XMLDOM");
} else if ( document.implementation && document.implementation.createDocument ) {
oXmlDoc = document.implementation.createDocument("", "", null);
}
IE/FF (xml file)
§Using XMLDOMObject. getElementsByTagName(..)
FF (xml string)
§var oDomParser=new DOMParser();
§var oDoc = oDomParser.parseFromString(XMLSTRING,"text/xml");


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