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A put option is a contract that gives its owner the right to sell an asset at a future date at a predetermined price.
Also note the use of _call.call(_toString, original) rather than simply original.toString(). This is because original.toString might itself be hooked by the time spoof is called. By holding cached references to Function.prototype.call and Function.prototype.toString at the very beginning of the script (before any page code runs), and invoking them via those cached references, the spoof function is immune to any tampering that might have happened in the interim. It’s eating its own tail in the most delightful way.