JavaScript Why is this variable undefined in the function? [duplicate] this variable undefined javascript,this variable is undefined mathcad,this

This question already has answers here:
Answer:1

The scope of a variable is the reason why you're seeing this. From the MDN documentation on var:

var hoisting

Because variable declarations (and declarations in general) are processed before any code is executed, declaring a variable anywhere in the code is equivalent to declaring it at the top. This also means that a variable can appear to be used before it's declared. This behavior is called "hoisting", as it appears that the variable declaration is moved to the top of the function or global code.

Variables in JavaScript are function-scoped, meaning they only exist in the function. Since variable declarations are processed before any execution of code, they are declared are the beginning of the enclosing function-scope. This "pre-processing" is called "hoisting", as the declaration is hoisted up to the beginning of the enclosing function-scope. Since you redeclare t inside the function, it's declared at the beginning of the function (because variables are function-scoped) and is equivalent to this:

var t = 20;
function test () {
    var t;
    console.log(t);
    t = 100;
}
test();

Since t is never given a value before you assign it after the logging, it's undefined. The solution is to remove the var redeclaration. Thus, no declaration of a variable is seen in the function and nothing is hoisted.


Note that this hoisting procedure is the same reason why you can use function declarations before they're defined:

foo(); //logs "foo called!"

function foo() {
    console.log("foo called!");
}
Answer:2

This seems like such a straight-forward thing to do, but I can't find a jQuery function to handle this. For example, $('div').show().sayHi() function sayHi(obj) { obj.html('hi') } sayHi() is ...

This seems like such a straight-forward thing to do, but I can't find a jQuery function to handle this. For example, $('div').show().sayHi() function sayHi(obj) { obj.html('hi') } sayHi() is ...

  1. call custom function powershell
  2. call custom function in jquery
  3. call custom function in wordpress
  4. call custom function in controller laravel
  5. call custom function in linq query
  6. call custom function matlab
  7. call custom function on click jquery
  8. call custom function vba
  9. call custom function sql
  10. call custom function javascript
  11. call custom function in excel
  12. call custom function spreadsheet
  13. call custom function
  14. call custom function onclick
  15. call custom function oracle
  16. calling custom function in r
  17. excel call custom function from cell
  18. call custom python function from matlab
  19. python call custom function
  20. jquery call custom function onclick

I have a fixed background, and a div with an absolute position in it; I would like to place it at the top: 5px and left: 5px, It's working when I have no rotation of the text, but I want to get my ...

I have a fixed background, and a div with an absolute position in it; I would like to place it at the top: 5px and left: 5px, It's working when I have no rotation of the text, but I want to get my ...

  1. rotation absolute
  2. rotation absolute value
  3. rotation absolute reference frame
  4. rotation absolute relative
  5. rotation absolute motion

Maybe the answer is obvious, but I don't get it. Why are the Dates in the Code Snippet different? Does the format say something about the hours as well? console.log("2017-1-9 -->") console....

Maybe the answer is obvious, but I don't get it. Why are the Dates in the Code Snippet different? Does the format say something about the hours as well? console.log("2017-1-9 -->") console....

  1. what does same date mean

I am learning javascript and at the same time trying to create a simple script that allows you to type a foreign language on a web browser with your keyboard. So, when you type a for example, there ...

I am learning javascript and at the same time trying to create a simple script that allows you to type a foreign language on a web browser with your keyboard. So, when you type a for example, there ...