The analogous code in Javascript for resizing and keeping data intact, similar to V

Question

The analogous code in Javascript for resizing and keeping data intact, similar to V

Currently, I am in the process of converting some older VBScript to Javascript for an ASP.NET project and there is a particular line that has me a bit stumped, as I am not entirely clear on its purpose.

The main function of the application is to allow users to input a new employee number into the database and then assign user permissions. The code I inherited is quite messy, but I am determined to get it functioning properly in Chrome.

Here is a snippet of the code that I have successfully translated so far:


if(form1.txtEmpno.value != ""){
var oOption;
oOption = document.createElement("OPTION");
oOption.text=form1.txtEmpno.value;
oOption.value=form1.txtEmpno.value;
form1.lstActive.add (oOption);
oOption = document.createElement("OPTION");
oOption.text="";
oOption.value="";
form1.lstPerms.add (oOption);
redim preserve arrUsers(1,ubound(arrUsers,2)+1);
arrUsers(0,ubound(arrUsers,2)) = form1.txtEmpno.value;
arrUsers(1,ubound(arrUsers,2)) = "";
form1.txtEmpno.value = "";
oOption = null;
}

And here is the specific line causing uncertainty:

redim preserve arrUsers(1,ubound(arrUsers,2)+1);

javascript asp.net arrays vbscript vb6-migration

Answer 1

Answer №1

According to MSDN, the

ReDim [Preserve] varname(subscripts)

statement is used to resize a dynamic array that has been declared using a Private, Public, or Dim statement without dimension subscripts. It can be repeatedly used to change the number of elements and dimensions in an array.

If the Preserve keyword is used, only the last array dimension can be resized without changing the number of dimensions. This means if there is only one dimension, it can be resized as it's the last one. However, for arrays with two or more dimensions, only the last dimension's size can be changed while preserving the contents of the array.

In JavaScript, arrays have different semantics compared to VBScript arrays. They are more similar to vectors than true arrays. Unlike VBScript, JavaScript does not support true N-dimensional arrays; instead, staggered-arrays (arrays-within-arrays) are used. Therefore, syntactically converting VBScript code to JavaScript may not be straightforward.

The relevant VBScript code snippet provided involves a 2-dimensional array named arrUsers. To convert this into a staggered array in JavaScript, modifications need to be made to accommodate the differences between the two languages.

A simpler approach in JavaScript could involve utilizing function-properties like push and pop for array manipulation:

var arrUsers = [ [], [] ]; // creating an empty, staggered 2-dimensional array
...
arrUsers[0].push( form1.txtEmpno.value );
arrUsers[1].pop();

If the array is primarily used to store and represent data within an internal model, leveraging JavaScript object prototypes might provide a more descriptive and efficient solution:

var User = function(empNo, name) {
    this.employeeNumber = empNo;
    this.name = name;
};

var users = [];
users.push( new User(1, "user 1") );
users.push( new User(23, "user 23") );

...

for(var i = 0; i < users.length; i++ ) {
    alert( users[i].name );
}

Answer 2

According to MSDN, the

ReDim [Preserve] varname(subscripts)

statement is used to resize a dynamic array that has been declared using a Private, Public, or Dim statement without dimension subscripts. It can be repeatedly used to change the number of elements and dimensions in an array.

If the Preserve keyword is used, only the last array dimension can be resized without changing the number of dimensions. This means if there is only one dimension, it can be resized as it's the last one. However, for arrays with two or more dimensions, only the last dimension's size can be changed while preserving the contents of the array.

In JavaScript, arrays have different semantics compared to VBScript arrays. They are more similar to vectors than true arrays. Unlike VBScript, JavaScript does not support true N-dimensional arrays; instead, staggered-arrays (arrays-within-arrays) are used. Therefore, syntactically converting VBScript code to JavaScript may not be straightforward.

The relevant VBScript code snippet provided involves a 2-dimensional array named arrUsers. To convert this into a staggered array in JavaScript, modifications need to be made to accommodate the differences between the two languages.

A simpler approach in JavaScript could involve utilizing function-properties like push and pop for array manipulation:

var arrUsers = [ [], [] ]; // creating an empty, staggered 2-dimensional array
...
arrUsers[0].push( form1.txtEmpno.value );
arrUsers[1].pop();

If the array is primarily used to store and represent data within an internal model, leveraging JavaScript object prototypes might provide a more descriptive and efficient solution:

var User = function(empNo, name) {
    this.employeeNumber = empNo;
    this.name = name;
};

var users = [];
users.push( new User(1, "user 1") );
users.push( new User(23, "user 23") );

...

for(var i = 0; i < users.length; i++ ) {
    alert( users[i].name );
}

The analogous code in Javascript for resizing and keeping data intact, similar to V

Answer №1

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