Chapter 02 of the book Mostly Adequate Guide to Functional Programming

Author: imteekay

javascript/mostly_adequate_guide_to_functional_programming/ch02.js

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+// Chapter 02: First Class Functions
+
+const hi = name => `Hi ${name}`;
+
+// const greeting = name => hi(name);
+// this is totally redundant,
+// because we can treat the greeting function as a value
+// and assign this value to the new greeting function, like that:
+
+const greeting = hi;
+
+// and use it normal function
+greeting('TK'); // Hi TK
+
+// Another more complex example
+// This function `const getServerStuff = callback => ajaxCall(json => callback(json));` is the same as this:
+const getServerStuff = ajaxCall;
+
+// Simplifying this function:
+// 1.  const getServerStuff = callback => ajaxCall(json => callback(json));
+// 2.  const getServerStuff = callback => ajaxCall(callback);
+// 3   const getServerStuff = ajaxCall;
+
+// Treating functions as values (first class), it easier to maintain.
+// If we have a wrapped function and it needs to change, we need to change both the wrapped function and the call
+
+// We have this httpGet function
+httpGet('/post/2', json => renderPost(json));
+
+// But we need to change the renderPost function to receive not only the json, but also the error (err)
+// We change the renderPost function and the calling
+httpGet('/post/2', json, err => renderPost(json, err));
+
+// Another approach is to treat functions as values and return the renderPost function
+// This way we only need to change the renderPost function. The httpGet function stays the same
+httpGet('/post/2', renderPost);