December 2015
Beginner to intermediate
276 pages
5h 15m
English
Content preview from You Don't Know JS: ES6 & Beyond
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Chapter 7. Meta Programming
Meta programming is programming where the operation targets the behavior of the program itself. In other words, it’s programming the programming of your program. Yeah, a mouthful, huh?
For example, if you probe the relationship between one object a and
another b—are they [[Prototype]] linked?—using
a.isPrototype(b), this is commonly referred to as introspection, a
form of meta programming. Macros (which don’t exist in JS, yet)—where
the code modifies itself at compile time—are another obvious example
of meta programming. Enumerating the keys of an object with a for..in
loop, or checking if an object is an instance of a “class
constructor,” are other common meta programming tasks.
Meta programming focuses on one or more of the following: code inspecting itself, code modifying itself, or code modifying default language behavior so other code is affected.
The goal of meta programming is to leverage the language’s own intrinsic capabilities to make the rest of your code more descriptive, expressive, and/or flexible. Because of the meta nature of meta programming, it’s somewhat difficult to put a more precise definition on it than that. The best way to understand meta programming is to see it through examples.
ES6 adds several new forms/features for meta programming on top of what JS already had.
Function Names
There are cases where your code may want to introspect on itself and ask what the name of some function is. If you ask what a function’s name is, ...
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