為什麼只有在 IE9 中開啟開發人員工具時，window.console.log 才可用？

IE9's Elusive Console.log: A Conditional Presence

In Internet Explorer 9, the existence of window.console.log presents an intriguing riddle. This article delves into the enigmatic nature of this function and explores the circumstances that govern its presence and behavior.

Window.console.log in IE9: An Incomplete Picture

Within IE9's strict confines, the window.console.log function is only granted access to the global scope if the developer tools curtain is gracefully parted for a given tab. However, this transient manifestation is not static. As you navigate the boundless web, the console object remains a constant companion, provided your developer tools window is not unceremoniously dismissed. But alas, a new tab demands a fresh pact with the developer tools to unveil the elusive console.

Why No Harmony with apply and call?

The riddle deepens when we consider the peculiar absence of window.console.log.apply and window.console.log.call. This discord stems from the console object's unique nature as a host object, one that proudly chooses not to inherit from Object or derive its methods from Function like its ECMAScript counterparts. Alas, IE9's imperfect embrace of DOM object conformity left the developer tools in a state of isolation, robbed of the same blessings bestowed upon their companions.

A Ray of Hope: Bind to the Rescue

Despite these limitations, a glimmer of hope emerges from the depths of Function.prototype.bind. This magical incantation empowers us to forge a harmonious bond between console methods and Function.prototype methods. Behold the following trickery:

var log = Function.prototype.bind.call(console.log, console);
log.apply(console, ["this", "is", "a", "test"]); //-> "thisisatest"

And there you have it, the art of invoking console methods with a dash of Function.prototype sorcery.

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