Code snippets

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Revision as of 11:04, 8 July 2007 by 146.151.111.140 (talk)
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Shortcut to document.getElementById

function $(id) {
  return document.getElementById(id);
}

Example usage:

$("header").innerHTML = "Halloa!";


XPath helper

Run a particular XPath expression p against the context node context (or the document, if not provided).

Returns the results as an array.

function $x(p, context) {
  if (!context) context = document;
  var i, arr = [], xpr = document.evaluate(p, context, null, XPathResult.UNORDERED_NODE_SNAPSHOT_TYPE, null);
  for (i = 0; item = xpr.snapshotItem(i); i  ) arr.push(item);
  return arr;
}

Example usage (with Array.forEach):

var paragraphs = $x("//p");
paragraphs.forEach(function(paragraph) {  // Loop over every paragraph
  paragraph.innerHTML = "Halloa!";
});

Note: When you specify a context node, you need to use a relative XPath expression.

Get elements by CSS selector

Lets you run an XPath using the concise CSS style selectors such as .class and #id, it also adds a much needed method of comparing the ends of strings, $=.

function $$(xpath,root) { 
  xpath=xpath.replace(/((^|\|)\s*)([^/|\s] )/g,'$2.//$3').
             replace(/\.([\w-] )(?!([^\]]*]))/g,'[@class="$1" or @class$=" $1" or @class^="$1 " or @class~=" $1 "]').
              replace(/#([\w-] )/g,'[@id="$1"]').
              replace(/\/\[/g,'/*[');
  str='(@\\w |"[^"]*"|\'[^\']*\')'
  xpath=xpath.replace(new RegExp(str '\\s*~=\\s*' str,'g'),'contains($1,$2)').
              replace(new RegExp(str '\\s*\\^=\\s*' str,'g'),'starts-with($1,$2)').
              replace(new RegExp(str '\\s*\\$=\\s*' str,'g'),'substring($1,string-length($1)-string-length($2) 1)=$2');
  var got=document.evaluate(xpath,root||document,null,null,null), result=[];
  while(next=got.iterateNext()) result.push(next);
  return result;
}


Example usage:

$$('#title')[0].innerHTML='Greased';
$$('a[@href $= "user.js"]').forEach(function (a) {
  a.innerHTML='check it out a script';
}
$$('a[@href ^= "http"]').forEach(function (a) {
  a.innerHTML  = ' (external)';
}

Conditional logging

Used to easily toggle sending debug messages to the console. Passes all arguments on to console.log, but only if console is defined (for backward compatibility) and DEBUG is true.

Code and example usage:

const DEBUG = true;

var links = document.links;
debug("Links: %o", links);

function debug() {
  if (DEBUG