@@ -298,6 +298,74 @@ dateAddMonth(date, 1);
 ```
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+### Functions should only be one level of abstraction
+When you have more than one level of abstraction your function is usually
+doing too much. Splitting up functions leads to reusability and easier
+testing.
+
+**Bad:**
+```javascript
+function parseBetterJSAlternative(code) {
+let REGEXES = [
+// ...
+];
+
+let statements = code.split(' ');
+let tokens;
+REGEXES.forEach((REGEX) => {
+statements.forEach((statement) => {
+// ...
+})
+});
+
+let ast;
+tokens.forEach((token) => {
+// lex...
+});
+
+ast.forEach((node) => {
+// parse...
+})
+}
+```
+
+**Good**:
+```javascript
+function tokenize() {
+let REGEXES = [
+// ...
+];
+
+let statements = code.split(' ');
+let tokens;
+REGEXES.forEach((REGEX) => {
+statements.forEach((statement) => {
+// ...
+})
+});
+
+return tokens;
+}
+
+function lexer() {
+let ast;
+tokens.forEach((token) => {
+// lex...
+});
+
+return ast;
+}
+
+function parseBetterJSAlternative(code) {
+let tokens = tokenize(code);
+let ast = lexer(ast);
+ast.forEach((node) => {
+// parse...
+})
+}
+```
+**[⬆ back to top](#table-of-contents)**
+
 ### Remove duplicate code
 Never ever, ever, under any circumstance, have duplicate code. There's no reason
 for it and it's quite possibly the worst sin you can commit as a professional