Is it possible to determine the size of an array using the eval() function?

Question

Is it possible to determine the size of an array using the eval() function?

How come this is not functioning as expected?

var issue_0 = ["a","b","c","d"];
arrayname = "issue_0";
arraylength = eval([arrayname]).length;
for (i = 0; i < arraylength; i++) {

I'm attempting to access different arrays based on user input, so I require arrayname to be a string that can be altered using code. However, eval([arrayname]).length is returning "1". What could be causing this discrepancy?

javascript arrays

Answer 1

Answer №1

Avoid using the eval function when the array has a global scope.

var items = ["x","y","z"];
arrayVariable = "items";
alert(window[arrayVariable].length);

Another option is to utilize the this keyword.

var nums = [5,6];
var stringVar = "nums";
alert(this[stringVar].length); //outputs 2

Answer 2

Avoid using the eval function when the array has a global scope.

var items = ["x","y","z"];
arrayVariable = "items";
alert(window[arrayVariable].length);

Another option is to utilize the this keyword.

var nums = [5,6];
var stringVar = "nums";
alert(this[stringVar].length); //outputs 2

Answer 3

Answer №2

Avoid using eval in your code - it may not be evil, but the inner workings are known to only a select few individuals. (And one of them may have even forgotten...)

Throughout my decade of experience with javascript programming, I've never found myself resorting to eval - there are alternative approaches at hand.

As evident from previous responses, there is no requirement for its usage in this particular scenario.

Answer 4

Avoid using eval in your code - it may not be evil, but the inner workings are known to only a select few individuals. (And one of them may have even forgotten...)

Throughout my decade of experience with javascript programming, I've never found myself resorting to eval - there are alternative approaches at hand.

As evident from previous responses, there is no requirement for its usage in this particular scenario.

Answer 5

Answer №3

Avoid using eval() as it is considered harmful. Instead of using eval, pass the array as an argument to a function that can determine its length based on the argument name. This simple approach will solve the problem without relying on unsafe practices.

var a1 = [0,1,2,3,4,5];
var a2 = [0,1,2,3];
var a3 = [0,1,];

function getArrayLength(a){
    return a.length;
}

getArrayLength(a1);
getArrayLength(a2);
getArrayLength(a3);

Check out this code snippet for a better solution.

In your original code, the issue lies in writing: eval([arrayname]).length. The correct way to access the length of an array using eval is: eval(arrayname).length, which evaluates the string as an object reference and retrieves the length of its members.

The following example demonstrates how the incorrect eval version could potentially be used, but remember to avoid using eval for real scenarios:

var problem_0 = ["a","b","c","d"];
arrayStringName = "problem_0";
arrayObjectName = eval(arrayStringName);
arraylength = arrayObjectName.length;
for (i = 0; i < arraylength; i++) { 
    alert(arrayObjectName[i]);
}

Explore this link for a demonstration.

Answer 6

Avoid using eval() as it is considered harmful. Instead of using eval, pass the array as an argument to a function that can determine its length based on the argument name. This simple approach will solve the problem without relying on unsafe practices.

var a1 = [0,1,2,3,4,5];
var a2 = [0,1,2,3];
var a3 = [0,1,];

function getArrayLength(a){
    return a.length;
}

getArrayLength(a1);
getArrayLength(a2);
getArrayLength(a3);

Check out this code snippet for a better solution.

In your original code, the issue lies in writing: eval([arrayname]).length. The correct way to access the length of an array using eval is: eval(arrayname).length, which evaluates the string as an object reference and retrieves the length of its members.

The following example demonstrates how the incorrect eval version could potentially be used, but remember to avoid using eval for real scenarios:

var problem_0 = ["a","b","c","d"];
arrayStringName = "problem_0";
arrayObjectName = eval(arrayStringName);
arraylength = arrayObjectName.length;
for (i = 0; i < arraylength; i++) { 
    alert(arrayObjectName[i]);
}

Explore this link for a demonstration.

Is it possible to determine the size of an array using the eval() function?

Answer №1

Answer №2

Answer №3

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