Constructors (in fact, all functions) automatically get a property named prototype, which by default holds a plain, empty object that derives from Object.prototype.

There is a method similar to apply, called call. It also calls the function it is a method of but takes its arguments normally, rather than as an array. Like apply and bind, call can be passed a specific this value.

A pure function is a specific kind of value-producing function that not only has no side effects but also doesn’t rely on side effects from other code—for example, it doesn’t read global variables that are occasionally changed by other code.

The basic rule, which has been repeated by many programmers and with which I wholeheartedly agree, is to not worry about efficiency until you know for sure that the program is too slow. If it is, find out which parts are taking up the most time, and start exchanging elegance for efficiency in those parts.

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lexical scoping

By treating function-local variables as existing only within the function, the language makes it possible to read and understand functions as small universes, without having to worry about all the code at once.

This means, for example, that the result variable in the power example will be newly created every time the function is called, and these separate incarnations do not interfere with each other.

A function can have multiple parameters or no parameters at all. In the following example, makeNoise does not list any parameter names, whereas power lists two: