JavaScript Function Context Incorrect

by

Context in Javascript is always established by the way you call a function.

var fn = ''.toUpperCase.call

This assigns the prototype implementation of the call function to fn. If you now call fn(), there’s no context to the call. call would try to invoke the function object it was associated with. However, that context is established at call time. Since you’re not giving it any context at call time, some internal component of call is throwing an error.

You’d have to do this:

fn.call(''.toUpperCase)

That’s right, you call the call function, establishing a context, namely the toUpperCase string function. In this specific case this would lead to another error inside toUpperCase, since it is not bound to a specific context. You’d need to establish that context explicitly as well:

var fn = ''.toUpperCase.call
fn.call(''.toUpperCase.bind(''))

Also see How does the “this” keyword work?

More Related Contents:

  1. How “==” works in JavaScript? [duplicate]
  2. show links when mouse over text [closed]
  3. Firebase query if child of child contains a value
  4. Merge/flatten an array of arrays
  5. Fastest way to flatten / un-flatten nested JSON objects
  6. Check whether variable is number or string in JavaScript
  7. var self = this?
  8. Difference between JSON.stringify and JSON.parse
  9. How do I do OuterHTML in firefox?
  10. JavaScript – Get minutes between two dates
  11. Conversion between UTF-8 ArrayBuffer and String
  12. How to prevent moment.js from loading locales with webpack?
  13. React – State not updated
  14. React Native: Getting the position of an element
  15. How can I dynamically unload a javascript file?
  16. Is possible to debug dynamic loading JavaScript by some debugger like WebKit, FireBug or IE8 Developer Tool?
  17. How to get an element’s top position relative to the browser’s viewport?
  18. Is it a good practice using Observable with async/await?
  19. How to dynamically modify in materialize css framework
  20. Converting a recursive function into an asynchronous CPS implementation (javascript)
  21. google chrome extension :: console.log() from background page?
  22. How to read line by line of a text area HTML tag
  23. Call Javascript function from URL/address bar
  24. Looping through jQuery Deferreds after all promises have been called
  25. Module not found: Error: Can’t resolve ‘fs’ in
  26. Javascript errors from Google Adsense
  27. Hour difference between two times(HH:MM:SS a)in momentjs
  28. Custom Legend with ChartJS v2.0
  29. Insert hyphens in JavaScript
  30. Angular 2 Final Release Router Unit Test

Leave a Comment