What is this asm style “x | 0” some javascript programmers are now using?

by

According to JavaScript Performance for Madmen

Wrapping integer arithmetic expressions in ( ) | 0 allows the runtime to be sure that you’re doing integer arithmetic instead of floating-point arithmetic. This allows it to avoid checking for overflow and produce faster code in many cases.

and according to the page, it’s true for “most” Javascript runtimes, but doesn’t say which.

As a second source, Writing Fast JavaScript For Games & Interactive Applications states

To tell JavaScript engine we want to store integer values […] we could use bitwise or operator:

and a third source from Microsoft’s Writing efficient JavaScript page:

[…] explicitly tell the JavaScript runtime to use integer arithmetic […] use the bitwise or operator

Also, apart from in comments, none of the pages above mention asm.js, so I suspect such optimizations apply in code not explicitly marked as asm/in browsers that don’t explicitly recognize it.

More Related Contents:

  1. "&" and ">>" number operator in C++?
  2. Which “href” value should I use for JavaScript links, “#” or “javascript:void(0)”?
  3. Where to place JavaScript in an HTML file?
  4. What does a tilde do when it precedes an expression?
  5. Long processing time likely due to getValue and cell inserts
  6. Are eval() and new Function() the same thing?
  7. Detect If Browser Tab Has Focus
  8. Ternary operators in JavaScript without an “else”
  9. Optimum way to compare strings in JavaScript? [duplicate]
  10. Unobtrusive JavaScript: at the top or the bottom of the HTML code?
  11. Does use of anonymous functions affect performance?
  12. What is the difference between Unary Plus/Number(x) and parseFloat(x)?
  13. Combine and Minify Multiple CSS / JS Files
  14. Unsigned Integer in Javascript
  15. bitwise AND in Javascript with a 64 bit integer
  16. How to do bitwise AND in javascript on variables that are longer than 32 bit?
  17. Why most JavaScript native functions are slower than their naive implementations?
  18. Why is iterating through an array backwards faster than forwards
  19. Javascript Performance: While vs For Loops
  20. Does the tag position in HTML affects performance of the webpage?
  21. Is optimizing JavaScript for loops really necessary?
  22. Two arrays, where items in array x can be in array y but not vice versa, test all permutations
  23. ES6 Tail Recursion Optimisation Stack Overflow
  24. Javascript Tilde & Two’s complement
  25. Optimize long lists of fixed string alternatives in regex
  26. HTML5 Canvas Performance and Optimization Tips, Tricks and Coding Best Practices [closed]
  27. Javascript (jQuery) performance measurement and best practices (not load time)
  28. What are some good css and js minimizers for production code? [closed]
  29. requestAnimationFrame garbage collection
  30. Unsigned Right Shift / Zero-fill Right Shift / >>> in PHP (Java/JavaScript equivalent)

Leave a Comment