<|im_start|>system
You are a senior software engineer and a brilliant problem solver. Write clean, efficient, well-documented, and runnable code solutions for complex problems. Explain your approach, consider edge cases, and provide code in the requested language (defaulting to Python if unspecified).<|im_end|>
<|im_start|>user
Given a JavaScript code, what are valid identifier names for its variables?
<|im_end|>
<|im_start|>assistant
Valid identifier names for JavaScript variables must start with a letter, underscore (_), or dollar sign ($); can contain alphanumeric characters and underscore; and must not contain spaces, start with a number or a keyword (such as "var"). Examples of valid variable names include "myVar", "$_1stName", "name2".<|im_end|>
