By Opera Software

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This method can be used to override global functions defined by regular scripts in a page.


  • name: String giving the name of the function to be overridden.
  • implementation: Function to be run in place of the function defined by the page. The function will be passed the following parameters.
    • A reference to the real function defined by the page.
    • The object that would have been referred to by the this keyword in the real function.
    • Any parameters that would have been passed to the real function (each is passed as a separate parameter to the magic function).


void defineMagicFunction (<DOMString> name, <Function> implementation)


window.opera.defineMagicFunction('getLayer', function (oRealFunc, oThis, oParam1, oParam2) {
  return oParam1.getElementById(oParam2).style;

// This example overrides a function f. If the this object refers to the window object, it returns false.
// Otherwise it just runs the real function instead:
window.opera.defineMagicFunction('f', function (real, thisObject) {
  if (thisObject == window) {
    return false;
  } else {
    return real.apply(thisObject, Array.prototype.slice.call(arguments, 2));

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    Matthias N

    Wednesday, August 8, 2012

    Calling a magic function will fail, if this call happens a second time by recursion.
    It doen't matter how deep this recursion is nested.
    As there exists no possibility to undefine a magic function, please do not use it on abovementioned functions.

    For a more detailed, but still unresolved discussion, check:
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