Please consult section .

4.2. How do I find out what JavaScript features are supported where?

This book usually mentions if a feature is part of ECMAScript 5 (as required by older browsers) or a newer version. For more detailed information (incl. pre-ES5 versions), there are several good compatibility tables available online:

• (by kangax, , zloirock)
• (by William Kapke)
• Mozilla’s have tables for each feature that describe relevant ECMAScript versions and browser support.

• Section “The TC39 process” describes how upcoming features are planned.
• Section answers various questions regarding upcoming features.

4.4. Why does JavaScript fail silently so often?

JavaScript often fails silently. Let’s look at two examples.

First example: If the operands of an operator don’t have the appropriate types, they are converted as necessary.

The reason for the silent failures is historical: JavaScript did not have exceptions until ECMAScript 3. Since then, its designers have tried to avoid silent failures.

The chapter on the history and evolution of JavaScript has a section that answers this question.

4.6. How can I quickly try out a piece of JavaScript code?