Trouble with 'this.function' and handling scope within my code

Question

Trouble with 'this.function' and handling scope within my code

Hi there! I'm having an issue with this code snippet:

Whenever I reach line 109, I encounter an error message that reads "TypeError: Result of expression 'this.allVarsDefined' [undefined] is not a function."

I find scope in javascript to be quite confusing. Could anyone take a look and see what my problem might be? Additionally, if you have any helpful articles or resources on learning about scope in javascript, please feel free to share them. This is my first time delving into JS, so any assistance would be greatly appreciated! :)

javascript ajax scope this

Answer 1

Answer №1

It appears that this code is likely prototype-based. To ensure your notification callback works correctly, consider setting it up like so:

setTimeout(this.notify.bind(this), 5000, track);

This will bind the notify function to the Scrobbler object, ensuring that this refers to the Scrobbler object rather than the event triggering the function when the timeout occurs.

If the assumption of using prototype is incorrect, a similar effect can be achieved using the following approach:

var that = this;
setTimeout( function() { that.notify(); }, 5000, track );

Answer 2

It appears that this code is likely prototype-based. To ensure your notification callback works correctly, consider setting it up like so:

setTimeout(this.notify.bind(this), 5000, track);

This will bind the notify function to the Scrobbler object, ensuring that this refers to the Scrobbler object rather than the event triggering the function when the timeout occurs.

If the assumption of using prototype is incorrect, a similar effect can be achieved using the following approach:

var that = this;
setTimeout( function() { that.notify(); }, 5000, track );

Answer 3

Answer №2

Consider making a modification to line 109 by

setTimeout(function(){this.notify()}, 5000, track);

This adjustment will create a "closure" (function(){this.notify()}) that encapsulates the "this" variable within it, including this.allVarsDefined, which should resolve the error you are encountering.

The issue with your previous code lies in simply extracting the function from the object instance when using "this.notify" and passing it to setTimeout without preserving any reference to the object itself. This approach is adequate if the notify function does not mention "this", but due to its reliance on "this", utilizing a closure is necessary.

For further understanding, I recommend delving into the concept of Javascript closures. You can find valuable insights in this article. Additionally, the book JavaScript: The Definitive Guide 5th Edition by O'Reilly is a highly recommended resource for mastering javascript programming at a reasonable price.

If the suggested solution does not resolve your issue, try simplifying your code to its essential components that you believe should work but are failing, and share it here for further assistance.

Answer 4

Consider making a modification to line 109 by

setTimeout(function(){this.notify()}, 5000, track);

This adjustment will create a "closure" (function(){this.notify()}) that encapsulates the "this" variable within it, including this.allVarsDefined, which should resolve the error you are encountering.

The issue with your previous code lies in simply extracting the function from the object instance when using "this.notify" and passing it to setTimeout without preserving any reference to the object itself. This approach is adequate if the notify function does not mention "this", but due to its reliance on "this", utilizing a closure is necessary.

For further understanding, I recommend delving into the concept of Javascript closures. You can find valuable insights in this article. Additionally, the book JavaScript: The Definitive Guide 5th Edition by O'Reilly is a highly recommended resource for mastering javascript programming at a reasonable price.

If the suggested solution does not resolve your issue, try simplifying your code to its essential components that you believe should work but are failing, and share it here for further assistance.

Trouble with 'this.function' and handling scope within my code

Answer №1

Answer №2

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