Does JavaScript have undefined behaviour?

by

There’s a lot of things in the spec that are explicitly left to the implementation. Especially when it comes to Host Objects, there can be many quirks. Examples that have nothing to do with host objects:

15.1 The Global Object

The values of the [[Prototype]] and [[Class]] internal properties of the global object are implementation-dependent.

15.1.2.2 parseInt (string , radix)

[If there are too many significant digits] mathInt may be an implementation-dependent approximation to the mathematical integer value that is represented by Z in radix-R notation.

15.3.4.2 Function.prototype.toString

An implementation-dependent representation of the function is returned.

Nearly all Date parse / stringifiy algorithms are implementation-dependent, this includes toLocaleString, toString, parse and the Date constructor.

15.4.4.11 Array.prototype.sort (comparefn) – likely the best example:

If comparefn is not undefined and is not a consistent comparison function for the elements of this array, the behaviour of sort is implementation-defined.

[…] If proto is not null and there exists an integer j such that all of the conditions below are satisfied then the behaviour of sort is implementation-defined:

  • obj is sparse (15.4)
  • 0 ≤ j < len

The behaviour of sort is also implementation defined if obj is sparse and any of the following conditions are true:

  • The [[Extensible]] internal property of obj is false.
  • Any array index property of obj whose name is a nonnegative integer less than len is a data property whose [[Configurable]] attribute is false.

The behaviour of sort is also implementation defined if any array index property of obj whose name is a nonnegative integer less than len is an accessor property or is a data property whose [[Writable]] attribute is false.

And most promiently:

Perform an implementation-dependent sequence of calls […]

15.5.4.9 String.prototype.localeCompare (that)

The two Strings are compared in an implementation-defined fashion

15.5.4.11 String.prototype.replace
[In replacement symbols, if the number is greater than the number of groups], the result is implementation-defined.

I’ll just stop listing here, you can search on through the spec. Other notable places may be the toLocaleString methods, or the implementation-dependent approximations returned by the Math methods.

More Related Contents:

  1. How can I convert a string to boolean in JavaScript?
  2. How to strip HTML tags from string in JavaScript? [duplicate]
  3. Check if a string is a date value
  4. Return from a promise then()
  5. Dynamic function name in javascript?
  6. How to avoid long nesting of asynchronous functions in Node.js
  7. How to prevent Javascript injection attacks within user-generated HTML
  8. Updating SVG Element Z-Index With D3
  9. How are JavaScript arrays represented in physical memory?
  10. Professional jQuery based Combobox control? [closed]
  11. How to register event with useEffect hooks?
  12. How do I create JavaScript array (JSON format) dynamically?
  13. How do I call a Javascript function from Python?
  14. can i be notified of cookie changes in client side javascript
  15. How can I detect an address bar change with JavaScript?
  16. Javascript equivalent of php’s strtotime()?
  17. Google Protocol Buffers: JavaScript Example
  18. Removing page title and date when printing web page (with CSS?)
  19. Are all JSON objects also valid JavaScript objects?
  20. Save and render a webpage with PhantomJS and node.js
  21. What is the defined execution order of ES6 imports?
  22. Trigger standard HTML5 validation (form) without using submit button?
  23. forEach loop through two arrays at the same time in javascript
  24. How to create an array of objects from multiple arrays
  25. Using elements that are added to an array with (document.getElementById(‘ID’))
  26. Console.log not working at all
  27. How to pass data from one page to another page html
  28. onDeviceReady not firing in PhoneGap hello world app
  29. Is there an “after submit” jQuery option?
  30. jQuery SVG vs. Raphael [closed]

Leave a Comment