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Benx Shen

A re-introduction to JavaScript - MDC - 1 views

developer.mozilla.org/..._re-introduction_to_JavaScript

javascript tutorial intro *精華* *i_love_it*

shared by Benx Shen on 14 Oct 09 - No Cached
  • var name = o && o.getName();
  • var name = otherName || "default";
  • The first argument to apply() is the object that should be treated as 'this'.
  • ...9 more annotations...
  • apply() has a sister function named call, which again lets you set 'this' but takes an expanded argument list as opposed to an array.
  • Closures
  • A closure is the combination of a function and the scope object in which it was created. Closures let you save state - as such, they can often be used in place of objects.
  • An unfortunate side effect of closures is that they make it trivially easy to leak memory in Internet Explorer.
  • The above code sets up the element to turn red when it is clicked. It also creates a memory leak. Why? Because the reference to el is inadvertently caught in the closure created for the anonymous inner function. This creates a circular reference between a JavaScript object (the function) and a native object (el).
  • delete el;
  • var clickHandler = function() { this.style.backgroundColor = 'red'; } (function() { var el = document.getElementById('el'); el.onclick = clickHandler; })();
  • Surprisingly, one trick for breaking circular references introduced by a closure is to add another closure:
  • It's useful to start with an idea of the language's history. JavaScript was created in 1995 by Brendan Eich, an engineer at Netscape, and first released with Netscape 2 early in 1996. It was originally going to be called LiveScript, but was renamed in an ill-fated marketing decision to try to capitalise on the popularity of Sun Microsystem's Java language — despite the two having very little in common. This has been a source of confusion ever since.
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